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use more string_view in utils

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there's a couple places that can be easily converted from using strings to using
string_views instead. gives a slight (~1%) boost to system eval.

 # before

  nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
    Time (mean ± σ):      2.946 s ±  0.026 s    [User: 2.655 s, System: 0.209 s]
    Range (min … max):    2.905 s …  2.995 s    20 runs

 # after

    Time (mean ± σ):      2.928 s ±  0.024 s    [User: 2.638 s, System: 0.211 s]
    Range (min … max):    2.893 s …  2.970 s    20 runs
This commit is contained in:
pennae 2022-01-12 16:02:29 +01:00
parent e61c4bc25a
commit 44c92a1667
3 changed files with 39 additions and 23 deletions
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18
src/libutil/util.hh
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@ -56,7 +56,7 @@ Path absPath(Path path,
double or trailing slashes. Optionally resolves all symlink
components such that each component of the resulting path is *not*
a symbolic link. */
Path canonPath(const Path & path, bool resolveSymlinks = false);
Path canonPath(PathView path, bool resolveSymlinks = false);
/* Return the directory part of the given canonical path, i.e.,
everything before the final `/'. If the path is the root or an
@ -368,15 +368,19 @@ MakeError(FormatError, Error);
/* String tokenizer. */
template<class C> C tokenizeString(std::string_view s, const string & separators = " \t\n\r");
template<class C> C tokenizeString(std::string_view s, std::string_view separators = " \t\n\r");
/* Concatenate the given strings with a separator between the
elements. */
template<class C>
string concatStringsSep(const string & sep, const C & ss)
string concatStringsSep(const std::string_view sep, const C & ss)
{
size_t size = 0;
// need a cast to string_view since this is also called with Symbols
for (const auto & s : ss) size += sep.size() + std::string_view(s).size();
string s;
s.reserve(size);
for (auto & i : ss) {
if (s.size() != 0) s += sep;
s += i;
@ -384,6 +388,14 @@ string concatStringsSep(const string & sep, const C & ss)
return s;
}
template<class ... Parts>
auto concatStrings(Parts && ... parts)
-> std::enable_if_t<(... && std::is_convertible_v<Parts, std::string_view>), string>
{
std::string_view views[sizeof...(parts)] = { parts... };
return concatStringsSep({}, views);
}
/* Add quotes around a collection of strings. */
template<class C> Strings quoteStrings(const C & c)