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| -rw-r--r-- | build2/variable | 23 |
1 files changed, 18 insertions, 5 deletions
diff --git a/build2/variable b/build2/variable index 8f0969a..a3c1ea6 100644 --- a/build2/variable +++ b/build2/variable @@ -77,11 +77,24 @@ namespace build2 // // The two variables are considered the same if they have the same name. // - // @@ Document override semantics. - // - // Note that we don't propagate variable type to override variables and we - // keep override values as untyped names. So they get "typed" when they are - // applied. + // If the variable is overridden on the command line, then override is the + // chain of the special override variables. Their names are derived from the + // main variable name as <name>.{__override,__prefix,__suffix} and they are + // not entered into the var_pool. The override variables only vary in their + // names and visibility. + // + // Note also that we don't propagate the variable type to override variables + // and we keep override values as untyped names. They get "typed" when they + // are applied. + // + // We use the "modify original, override on query" model. Because of that, a + // modified value does not necessarily represent the actual value so care + // must be taken to re-query after (direct) modification. And because of + // that, variables set by the C++ code are by default non-overridable. + // + // Initial processing including entering of global overrides happens in + // reset() before any other variables. Project wide overrides are entered in + // main(). Overriding happens in scope::find_override(). // struct variable { |