make completions const (#408)

* make some completion methods const

Author: hendrikmuhs

keyvi/.clang-tidy

@@ -11,8 +11,10 @@ Checks: "*,
         -readability-else-after-return,
         -readability-static-accessed-through-instance,
         -readability-avoid-const-params-in-decls,
+        -readability-magic-numbers,
         -cppcoreguidelines-non-private-member-variables-in-classes,
         -misc-non-private-member-variables-in-classes,
+        -cppcoreguidelines-avoid-magic-numbers,
 "
 HeaderFilterRegex: ''
 FormatStyle:     none

keyvi/CPPLINT.cfg

@@ -1,3 +1,3 @@
 linelength=120
 root=include
-filter=-build/include_subdir,-whitespace/indent_namespace,-build/c++17
+filter=-build/include_subdir,-whitespace/indent_namespace,-build/c++17,-readability/nolint

keyvi/include/keyvi/dictionary/completion/forward_backward_completion.h

@@ -35,6 +35,7 @@
 #include <boost/algorithm/string.hpp>
 
 #include "keyvi/dictionary/completion/prefix_completion.h"
+#include "keyvi/dictionary/match_iterator.h"
 #include "keyvi/dictionary/util/bounded_priority_queue.h"
 
 // #define ENABLE_TRACING
@@ -56,7 +57,9 @@ class ForwardBackwardCompletion final {
     bool operator()(const match_t& m1, const match_t& m2) const { return m1->GetScore() < m2->GetScore(); }
   };
 
-  MatchIterator::MatchIteratorPair GetCompletions(const std::string& query, int number_of_results = 10) {
+  // NOLINTBEGIN(readability-function-cognitive-complexity)
+  [[nodiscard]] MatchIterator::MatchIteratorPair GetCompletions(const std::string& query,
+                                                                int number_of_results = 10) const {
     // get query length
     const size_t query_length = query.size();
 
@@ -252,9 +255,9 @@ class ForwardBackwardCompletion final {
 
       return match_t();
     };
-
     return MatchIterator::MakeIteratorPair(tfunc);
   }
+  // NOLINTEND(readability-function-cognitive-complexity)
 
  private:
   PrefixCompletion forward_completions_;

keyvi/include/keyvi/dictionary/completion/prefix_completion.h

@@ -26,6 +26,7 @@
 #define KEYVI_DICTIONARY_COMPLETION_PREFIX_COMPLETION_H_
 
 #include <algorithm>
+#include <cstddef>
 #include <memory>
 #include <string>
 #include <utility>
@@ -54,7 +55,8 @@ class PrefixCompletion final {
  public:
   explicit PrefixCompletion(dictionary_t d) : fsa_(d->GetFsa()) {}
 
-  MatchIterator::MatchIteratorPair GetCompletions(const std::string& query, size_t number_of_results = 10) {
+  [[nodiscard]] MatchIterator::MatchIteratorPair GetCompletions(const std::string& query,
+                                                                size_t number_of_results = 10) const {
     uint64_t state = fsa_->GetStartState();
     const size_t query_length = query.size();
     size_t depth = 0;