diff options
Diffstat (limited to 'libbuild2/in/init.cxx')
| -rw-r--r-- | libbuild2/in/init.cxx | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/libbuild2/in/init.cxx b/libbuild2/in/init.cxx index 6743e31..8bd5909 100644 --- a/libbuild2/in/init.cxx +++ b/libbuild2/in/init.cxx @@ -64,6 +64,22 @@ namespace build2 // vp.insert_alias (im, "in.substitution"); + // Substitution map. Substitutions can be specified as key-value pairs + // rather than buildfile variables. This map is checked before the + // variables. An absent value in key-value has the NULL semantics. + // + // This mechanism has two primary uses: Firstly, it allows us to have + // substitution names that cannot be specified as buildfile variables. + // For example, a name may start with an underscore and thus be + // reserved or it may refer to one of the predefined variables such a + // `include` or `extension` that may have a wrong visibility and/or + // type. + // + // Secondly, this mechanism allows us to encapsulate a group of + // substitutions and pass this group around as a single value. + // + vp.insert<map<string, optional<string>>> ("in.substitutions"); + // Fallback value to use for NULL value substitutions. If unspecified, // NULL substitutions are an error. // |