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#REDIRECT [[Polymorphic Types (PMTs)]]
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= Polymorphic Type =
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A new data type is a polymorphic data type. The type can really be used to store anything, but also has simple conversion methods for common data types such as bool, long, or a vector.
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The polymorphic type simplifies message passing between blocks, as all of the data is of the same type, including the message. Tags also use PMTs as data type, so a stream tag can be of any logical data type. In a sense, PMTs are a way to extend C++' strict typing with something more flexible.
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{{>toc}}
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== PMT Types ==
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The PMT library supports the following major types. Some of the more complex types have their own wiki page for assistance.
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'''''' ''bool'' - just like a C++ boolean, true or false
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'''''' ''symbol'' - easiest to think of it as a std::string
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'''''' ''integer'' - int, long, unsigned
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'''''' ''real'' - double, float
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'''''' ''complex'' - gr_complex, std::complex
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'''''' ''null'' - NULL
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'''''' ''pair'' - a 2-tuple data type
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'''''' ''list'' - a list
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'''''' ''vector'' - a vector of PMT objects
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'''''' ''dict'' - a dictionary (hash) like structure
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'''''' ''uniform_vector'' - a vector of typed objects (uint8_t, float, etc...)
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'''''' ''any'' - boost:any cast
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== Making a PMT instance ==
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To make PMT, the data type ''pmt_t'' is used just like any other data type.
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The following is an example:
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<pre>pmt_t p_instance;</pre>
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== Constructing/Assigning a PMT ==
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To construct or assign a value to a PMT, a method is available for each type of the following syntax: ''pmt''<type>_.
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The following constructors are available, all of which return ''pmt_t'':
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'''''' pmt_bool()
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'''''' pmt_symbol(const std::string &amp;)
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'''''' pmt_integer(long)
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'''''' pmt_real(double)
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'''''' pmt_complex(std::complex<double>)
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'''''' pmt_null()
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'''''' pmt_pair() or pmt_pair(pmt,pmt)
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'''''' pmt_vector(size_t,pmt)
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'''''' pmt_dict()
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'''''' pmt_make_'''vector(size_t,''') -- [[#UniformVectors|see uniform vectors]]
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'''''' pmt_any(const boost::any &amp;)
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For example, pmt_integer(long) returns a pmt_t, constructed from a long:
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<pre>pmt_t p_num = pmt_integer(3);</pre>
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== Checking PMT Type ==
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With a polymorphic type, it is useful to have methods to check what type it actually is if unknown.
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The following methods are available for testing PMT types, all of which return ''bool'':
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'''''' pmt_is_bool(pmt)
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'''''' pmt_is_symbol(pmt)
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'''''' pmt_is_number(pmt)
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'''''' pmt_is_integer(pmt)
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'''''' pmt_is_real(pmt)
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'''''' pmt_is_complex(pmt)
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'''''' pmt_is_null(pmt)
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'''''' pmt_is_pair(pmt)
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'''''' pmt_is_vector(pmt)
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'''''' pmt_is_uniform_vector(pmt)
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'''''' pmt_is_dict(pmt)
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'''''' pmt_is_any(pmt)
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In this example, ''test_pmt'' will be assigned the value ''true'':
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<pre>pmt_t p_num = pmt_integer(3);
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bool test_pmt = pmt_is_integer(p_num);</pre>
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== PMT Constants ==
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There are 3 main constant values in the PMT world which can be returned:
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'''''' ''PMT_T'' - PMT representation of true
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'''''' ''PMT_F'' - PMT representation of false
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'''''' ''PMT_NIL'' - PMT NIL/NULL representation
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When a PMT is initialized with no value, such as ''pmt_dict()'' ... it is equivalent to PMT_NIL until it is assigned elements.
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== Testing Equality ==
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To test the equality of PMT types, the following methods are available.
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'''''' ''pmt_eq(pmt_t, pmt_t)'' - tests strict equality (the two parameters are the same)
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'''''' ''pmt_eqv(pmt_t, pmt_t)'' - tests for equivalence (the two parameters have the same value)
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'''''' ''pmt_equal(pmt_t, pmt_t)'' - tests for equivalence of multi-value types (pmt_pair, pmt_vector)
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The following gives a good overview of equality testing:
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<pre>pmt_t p1 = pmt_integer(5);
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pmt_t p2 = pmt_integer(5);
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pmt_t p3 = pmt_integer(1);
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pmt_eq(p1, p1);  // Returns true
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pmt_eq(p1, p2);  // Returns false
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pmt_eqv(p1, p1); // Returns true
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pmt_eqv(p1, p2); // Returns true
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pmt_t p3 = pmt_pair(p1, p1);
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pmt_t p4 = pmt_pair(p1, p2);
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pmt_t p5 = pmt_pair(p1, p3);
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pmt_equal(p3, p4);  // Returns true, equivalence in values
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pmt_equal(p3, p5);  // Returns false, values are different</pre>
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== PMT Conversion Methods ==
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There are simple methods to store common C++ types as PMT for use in passing the data in m-block messages.
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All of the conversion methods are of a similar syntax:
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'''''' ''pmt_from''<type>_ - convert a C++ type to a PMT
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'''''' ''pmt_to''<type>_ - convert a PMT to a C++ type
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The following C++ types are supported:
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'''''' bool, long, double, complex
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For example:
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<pre>pmt_t p_val = pmt_from_long(3);
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long l_val = pmt_to_long(p_val);</pre>
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In Python, you can use the pmt.to_python() and pmt.to_pmt() methods to convert, without having to know the type yourself (see below).
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== Checking PMT Length ==
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For variable length PMT types, such as list and vector, you can use the following method to check how many elements are in the PMT:
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'''''' size_t pmt_length(pmt_t)
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<pre>pmt_t p1 = pmt_integer(1);
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pmt_t p2 = pmt_integer(2);
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pmt_t p3 = pmt_integer(3);
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pmt_t p_list = pmt_list3(p1, p2, p3);
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pmt_length(p_list);  // Returns 3</pre>
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== Detailed Type Information ==
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=== Lists ===
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PMT lists are as they sound, lists! Each list element is of type pmt_t, and the list can be of infinite length.
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To create a base list, you can use the following methods:
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'''''' pmt_list1(pmt_t)
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'''''' pmt_list2(pmt_t, pmt_t)
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'''''' pmt_list3(pmt_t, pmt_t, pmt_t)
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'''''' pmt_list4(pmt_t, pmt_t, pmt_t, ...)
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'''''' pmt_list5(pmt_t, pmt_t, pmt_t, ...)
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'''''' pmt_list6(pmt_t, pmt_t, pmt_t, ...)
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Anything beyond 6, use an add, which returns a new list:
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'''''' pmt_t pmt_list_add(pmt_t list, pmt_t object)
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List items cannot be removed, as they are implemented as constants.
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To access the nth element in a list, the following method is available which returns the nth element:
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'''''' pmt_t pmt_nth(size_t n, pmt_t list)
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The following exercises PMT lists:
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<pre>pmt_t p_list1 = pmt_list1(PMT_T);
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p_list1 = pmt_list_add(p_list1, PMT_F);
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pmt_t p_list2 = pmt_list2(PMT_T, PMT_F);
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pmt_equal(p_list1, p_list2);  // Returns true
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pmt_t p_element0 = pmt_nth(0, p_list2);  // Access elements
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pmt_t p_element1 = pmt_nth(1, p_list2);
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pmt_eqv(p_element0, PMT_T);  // Returns true
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pmt_eqv(p_element1, PMT_F);  // Returns true</pre>
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=== Uniform Vectors ===
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Uniform PMT vectors are for storing vectors of common C++ types. The following types are supported:
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'''''' uint8_t, int8_t, uint16_t, int16_t, uint32_t, int32_t, uint64_t, int64_t, float, double, std::complex<float>, std::complex<double>
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The following methods are used to create a uniform vector, whose return types are ''pmt_t'', where the first parameter is the number of elements to create and the second parameter is a fill parameter for initializing all of the elements to a specific value:
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'''''' pmt_make_u8vector(size_t, uint8_t)
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'''''' pmt_make_s8vector(size_t, int8_t)
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'''''' pmt_make_u16vector(size_t, uint16_t)
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'''''' pmt_make_s16vector(size_t, int16_t)
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'''''' pmt_make_u32vector(size_t, uint32_t)
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'''''' pmt_make_s32vector(size_t, int32_t)
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'''''' pmt_make_u64vector(size_t, uint64_t)
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'''''' pmt_make_s64vector(size_t, int64_t)
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'''''' pmt_make_f32vector(size_t, float);
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'''''' pmt_make_f64vector(size_t, double);
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'''''' pmt_make_c32vector(size_t, std::complex<float>)
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'''''' pmt_make_c64vector(size_t, std::complex<double>)
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To get a reference to each vector to access it like an array, you can use the following, which takes a uniform vector as parameter 1, and a pointer to a size_t to return the number of elements in the vector:
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'''''' pmt_<type>vector_ref(pmt_t, size_t)
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The following is an example of uniform vectors:
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<pre>static const int nelements = 64;
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pmt_t s16vec = pmt_make_s16vector(nelements, 0);  // Initializes all 64 elements to 0
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size_t vec_size;
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int16_t *elements = pmt_s16vector_writable_elements(s16vec, vec_size);  // Returns pointer, vec_size is set to 64
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// Now you can access the elements like a standard array
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for(int i=0; i</pre>
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=== Dictionaries ===
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A dictionary behaves exactly like a hash. PMT objects are referenced with a pmt_symbol (string-like PMT type).
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To create a dictionary, use:
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'''''' pmt_t pmt_make_dict()
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To set items in a dictionary, use:
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'''''' dict = pmt_dict_add(pmt_t dict, pmt_t symbol, pmt_t value)
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You can reference items in a dictionary using the following, which returns a specified ''error_val'' if the symbol (hash key) did not exist:
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'''''' pmt_dict_ref(pmt_t dict, pmt_t symbol, pmt_t error_val)
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It is always useful to check that a pmt_t is a dictionary before trying to reference its elements to prevent exceptions:
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'''''' pmt_is_dict(pmt_t)
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The following is an example of using dictionaries:
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<pre>pmt_t p_dict = pmt_make_dict();  // Empty dictionary
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p_dict = pmt_dict_add(p_dict, pmt_symbol(&quot;number of dogs&quot;), pmt_integer(3));
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p_dict = pmt_dict_add(p_dict, pmt_symbol(&quot;number of cats&quot;), pmt_integer(5));
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p_dict = pmt_dict_add(p_dict, pmt_symbol(&quot;has a dog&quot;), PMT_T);
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p_dict = pmt_dict_add(p_dict, pmt_symbol(&quot;has a turtle&quot;), PMT_F);
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if(pmt_is_dict(p_dict)) {
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  pmt_t p_ndogs = pmt_dict_ref(p_dict, pmt_symbol(&quot;number of dogs&quot;), PMT_NIL);
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  pmt_t p_ncats = pmt_dict_ref(p_dict, pmt_symbol(&quot;number of cats&quot;), PMT_NIL);
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  pmt_t p_dog = pmt_dict_ref(p_dict, pmt_symbol(&quot;has a dog&quot;), PMT_NIL);
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  pmt_t p_turtle = pmt_dict_ref(p_dict, pmt_symbol(&quot;has a turtle&quot;), PMT_NIL);
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  std::cout &lt;&lt; &quot;I have &quot; &lt;&lt; pmt_to_long(p_ndogs) &lt;&lt; &quot; dogs!\n&quot;;
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  std::cout &lt;&lt; &quot;I have &quot; &lt;&lt; pmt_to_long(p_ncats) &lt;&lt; &quot; cats!\n&quot;;
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  if(pmt_eqv(p_dog, PMT_T))
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    std::cout &lt;&lt; &quot;I have a dog\n&quot;;      // This will be outputted
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  else
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    std::cout &lt;&lt; &quot; I do not have a dog\n&quot;;
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  if(pmt_eqv(p_turtle, PMT_T))
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    std::cout &lt;&lt; &quot;I have a turtle\n&quot;;
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  else
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    std::cout &lt;&lt; &quot;I do not have a turtle\n&quot;;  // This will be outputted
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}</pre>
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=== Any ===
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When there is nothing to store your type, use a pmt_any. This allows you to cast anything into a pmt_t using boost::any cast.
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Example:
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<pre>typedef struct d_frame_hdr_t {
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  long src_addr;
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  long dst_addr;
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} +attribute+((+packed+));
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d_frame_hdr_t my_header;
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my_header.src_addr = 3;
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my_header.dst_addr = 4;
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pmt_t p_any = pmt_make_any(my_header);
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// After extracting using pmt_any_ref the following will be true:
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//  extract_header.src_addr == 3
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//  extract_header.dst_addr == 4
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d_frame_hdr_t extract_header = boost::any_cast (pmt_any_ref(p_any));</pre>
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== Conversion between Python Objects and PMTs ==
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Although PMTs can be manipulating in python using the python versions of the C++ interfaces there are some additional goodies that make it easier to work with PMTs in python.<br />
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In particular there are functions to automate the conversion of python booleans, strings, integers, longs, floats, complex numbers, dictionaries, lists, tuples and combinations thereof into their equivalent PMTs.<br />
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Two functions capture most of this functionality.
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* pmt.to_pmt - Converts a python object to a PMT.
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* pmt.to_python - Converts a PMT into a python object.

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