Using # define to implement multiple approximate codes-application in Map,set

within the STL, the Map,set is implemented using the same red-black tree, the map corresponds to the template parameter key_type,mapped_type, and the set The corresponding template parameter has no mapped_type

both support insert operations

Pair<iterator, bool> Insert (const value_type& value);

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for Map

typedef pair<key_type, mapped_type> Value_type;

for Set

Typdef Key_type Value_type;

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so in the extension library Pb_ds ( code in ext/pb_ds)

It 's designed like this, like trie.

Trie<string, int> says key is string,mapped is int

Trie<string, null_type> says that key is a string without mapped similar to a trieset concept.

so how to do this, such as writing a trie structure, how to better avoid triemap,trieset code duplication, while providing two kinds of implementations (Trieset No mapped takes up less space ).

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In addition to the template class commonly used techniques traits and tag forward , here to use the #define #endef skills, first look at the Folly of a

about the Fbvector 's test.

In the . h of test

Testfun (clause_23_3_6_1_1) {

VECTOR v;

Expect_true (V.empty ());

Vector::allocator_type A;

VECTOR v1 (a);

Expect_true (V1.empty ());

}

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in the cpp of test

typedef vector<int> Intvector;

typedef fbvector<int> Intfbvector;

typedef vector<folly::fbstring> Fbstringvector;

typedef fbvector<folly::fbstring> Fbstringfbvector

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#define VECTOR Intvector

#include <folly/test/FBVectorTestBenchmarks.cpp.h>//Nolint

#undef VECTOR

#define VECTOR Intfbvector

#include <folly/test/FBVectorTestBenchmarks.cpp.h>//Nolint

#undef VECTOR

#define VECTOR Fbstringvector

#include <folly/test/FBVectorTestBenchmarks.cpp.h>//Nolint

#undef VECTOR

#define VECTOR Fbstringfbvector

#include <folly/test/FBVectorTestBenchmarks.cpp.h>//Nolint

#undef VECTOR

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Pb_ds is a similar approach.

#define Pb_ds_data_true_indicator

#define PB_DS_V2F (x) (x).

#include <ext/pb_ds/detail/pat_trie_/pat_trie_.hpp>

#undef Pb_ds_data_true_indicator

#undef pb_ds_v2f

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#define Pb_ds_data_false_indicator

#define PB_DS_V2F (x) (x)

#include <ext/pb_ds/detail/pat_trie_/pat_trie_.hpp>

#undef Pb_ds_data_false_indicator

#undef pb_ds_v2f

Here's a look at the pat_trie_.hpp.

#ifdef Pb_ds_data_true_indicator

#define PB_DS_PAT_TRIE_NAME Pat_trie_map

#endif

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#ifdef Pb_ds_data_false_indicator

#define PB_DS_PAT_TRIE_NAME Pat_trie_set

#endif

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Template<typename Key, TypeName Mapped, TypeName Node_and_it_traits,

TypeName _alloc>

Class Pb_ds_pat_trie_name:

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In fact, two times, # include PAT_TRIE_.HPP, respectively, define

Pat_trie_map and Pat_trie_set

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look inside the class Pb_ds_pat_trie_name.

Inline std::p air<point_iterator, bool>

Insert (const_reference);

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Inline mapped_reference

Operator[] (key_const_reference r_key)

{

#ifdef Pb_ds_data_true_indicator

Return Insert (Std::make_pair (R_key, Mapped_type ())) .first->second;

#else

Insert (R_key);

return traits_base::s_null_type;

#endif

}

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look at the implementation of This insert pat_trie_/insert_join_fn_imps.hpp

Pb_ds_class_t_dec

Inline std::p air<typename pb_ds_class_c_dec::iterator, bool>

Pb_ds_class_c_dec::

Insert (Const_reference r_val)

{

Node_pointer P_LF = Find_imp(pb_ds_v2f (r_val));

if (p_lf! = 0 && P_lf->m_type = = Leaf_node &&

Synth_access_traits::equal_keys (pb_ds_v2f (static_cast<leaf_pointer> (P_LF)->value ()), PB_DS_V2F (r_ Val)))

{

Pb_ds_check_key_exists (pb_ds_v2f (R_val))

Pb_ds_assert_valid ((*this))

Return Std::make_pair (Iterator (P_LF), false);

}

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Pb_ds_check_key_does_not_exist (pb_ds_v2f (R_val))

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Leaf_pointer P_NEW_LF = s_leaf_allocator.allocate (1);

Cond_dealtor cond (P_NEW_LF);

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New (P_NEW_LF) leaf (r_val);

Apply_update (P_NEW_LF, (node_update*) this);

Cond.set_call_destructor ();

Branch_bag bag;

Bag.add_branch ();

M_p_head->m_p_parent = Rec_join (m_p_head->m_p_parent, P_NEW_LF, 0, bag);

M_p_head->m_p_parent->m_p_parent = M_p_head;

Cond.set_no_action_dtor ();

++m_size;

Update_min_max_for_inserted_leaf (P_NEW_LF);

_glibcxx_debug_only (Debug_base::insert_new (pb_ds_v2f (r_val));)

Pb_ds_assert_valid ((*this))

Return Std::make_pair (Point_iterator (P_NEW_LF), true);

}

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OK, that's what it means. when used in map pb_ds_v2f is x.first and set inside uses pb_ds_v2f is x itself.

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Using # define to implement multiple approximate codes-application in Map,set