Optimize variable extraction in bootstrap_src()

1 files changed, 8 insertions, 11 deletions

diff --git a/libbuild2/file.hxx b/libbuild2/file.hxx
index 3bceb80..f64f130 100644
--- a/libbuild2/file.hxx
+++ b/libbuild2/file.hxx
@@ -210,27 +210,24 @@ namespace build2
   load_root (scope& root);
 
   // Extract the specified variable value from a buildfile. It is expected to
-  // be the n'th non-blank/comment line and not to rely on any variable
+  // be the first non-blank/comment line and not to rely on any variable
   // expansions other than those from the global scope or any variable
-  // overrides. Return in second an indication of whether the variable was
-  // found.
+  // overrides. Return nullopt if the variable was not found.
   //
-  LIBBUILD2_SYMEXPORT pair<value, bool>
-  extract_variable (context&, const path&, const variable&, size_t n = 1);
+  LIBBUILD2_SYMEXPORT optional<value>
+  extract_variable (context&, const path&, const variable&);
 
   // As above, but extract from a stream. The path argument is used for
   // diagnostics.
   //
-  LIBBUILD2_SYMEXPORT pair<value, bool>
-  extract_variable (context&,
-                    istream&, const path&,
-                    const variable&, size_t = 1);
+  LIBBUILD2_SYMEXPORT optional<value>
+  extract_variable (context&, istream&, const path&, const variable&);
 
   // As above, but extract from a lexer (this could be useful for extracting
   // from stdin).
   //
-  LIBBUILD2_SYMEXPORT pair<value, bool>
-  extract_variable (context&, lexer&, const variable&, size_t = 1);
+  LIBBUILD2_SYMEXPORT optional<value>
+  extract_variable (context&, lexer&, const variable&);
 
   // Import has two phases: the first is triggered by the import directive in
   // the buildfile. It will try to find and load the project. Failed that, it