Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit e0da8a1d authored by Dan Albert's avatar Dan Albert
Browse files

Generalize Join to work for any container/element. 

This is more scalable than explicitly instantiating templates for the
cross product of containers and element types.

Specifically I'm adding this so I can join an unordered_set in adb.

Change-Id: I0055f3390a0ff26a886a0d41bbf0d4fe3d210f9c
parent 3ff23e24

base/include/base/strings.h

+19 −3
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#ifndef BASE_STRINGS_H

#define BASE_STRINGS_H



#include <sstream>

#include <string>

#include <vector>
@@ -34,9 +35,24 @@ std::vector<std::string> Split(const std::string& s, 
// Trims whitespace off both ends of the given string.

std::string Trim(const std::string& s);



// Joins a vector of strings into a single string, using the given separator.

template <typename StringT>

std::string Join(const std::vector<StringT>& strings, char separator);

// Joins a container of things into a single string, using the given separator.

template <typename ContainerT>

std::string Join(const ContainerT& things, char separator) {

  if (things.empty()) {

    return "";

  }



  std::ostringstream result;

  result << *things.begin();

  for (auto it = std::next(things.begin()); it != things.end(); ++it) {

    result << separator << *it;

  }

  return result.str();

}



// We instantiate the common cases in strings.cpp.

extern template std::string Join(const std::vector<std::string>&, char);

extern template std::string Join(const std::vector<const char*>&, char);



// Tests whether 's' starts with 'prefix'.

bool StartsWith(const std::string& s, const char* prefix);

base/strings.cpp

+4 −19
Original line number Diff line number Diff line
@@ -79,25 +79,10 @@ std::string Trim(const std::string& s) { 
  return s.substr(start_index, end_index - start_index + 1);

}



template <typename StringT>

std::string Join(const std::vector<StringT>& strings, char separator) {

  if (strings.empty()) {

    return "";

  }



  std::string result(strings[0]);

  for (size_t i = 1; i < strings.size(); ++i) {

    result += separator;

    result += strings[i];

  }

  return result;

}



// Explicit instantiations.

template std::string Join<std::string>(const std::vector<std::string>& strings,

                                       char separator);

template std::string Join<const char*>(const std::vector<const char*>& strings,

                                       char separator);

// These cases are probably the norm, so we mark them extern in the header to

// aid compile time and binary size.

template std::string Join(const std::vector<std::string>&, char);

template std::string Join(const std::vector<const char*>&, char);



bool StartsWith(const std::string& s, const char* prefix) {

  return s.compare(0, strlen(prefix), prefix) == 0;

base/strings_test.cpp

+13 −0
Original line number Diff line number Diff line
@@ -20,6 +20,8 @@ 


#include <string>

#include <vector>

#include <set>

#include <unordered_set>



TEST(strings, split_empty) {

  std::vector<std::string> parts = android::base::Split("", ",");
@@ -121,6 +123,17 @@ TEST(strings, join_separator_in_vector) { 
  ASSERT_EQ(",,,", android::base::Join(list, ','));

}



TEST(strings, join_simple_ints) {

  std::set<int> list = {1, 2, 3};

  ASSERT_EQ("1,2,3", android::base::Join(list, ','));

}



TEST(strings, join_unordered_set) {

  std::unordered_set<int> list = {1, 2};

  ASSERT_TRUE("1,2" == android::base::Join(list, ',') ||

              "2,1" == android::base::Join(list, ','));

}



TEST(strings, startswith_empty) {

  ASSERT_FALSE(android::base::StartsWith("", "foo"));

  ASSERT_TRUE(android::base::StartsWith("", ""));