diff options
Diffstat (limited to 'libbuild2/config/utility.hxx')
| -rw-r--r-- | libbuild2/config/utility.hxx | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx index bf4728f..cbfe588 100644 --- a/libbuild2/config/utility.hxx +++ b/libbuild2/config/utility.hxx @@ -91,10 +91,16 @@ namespace build2 // // Unlike the rest of the lookup_config() versions, this one leaves the // unspecified value as undefined rather than setting it to a default - // value. This can be useful when we don't have a default value or if we - // want the mentioning of the variable to be omitted from persistent + // value. This can be useful when we don't have a default value or in case + // we want the mentioning of the variable to be omitted from persistent // storage (e.g., a config file) if the default value is used. // + // Note also that we can first do the lookup without the default value and + // then, if there is no value, call the version with the default value and + // end up with the same result if we called the default value version + // straight away. This is useful when computing the default value is + // expensive. + // // @@ Should we pass flags and interpret save_null_omitted to treat null // as undefined? Sounds logical. // @@ -135,7 +141,9 @@ namespace build2 // The second version in addition sets the new_value argument as described // above. Note, however, that if the save_default_commented flag is // specified, then the default value is never considered "new" since for - // such variables absence of a value means it is the default value. + // such variables absence of a value means it is the default value. This + // flag is normally used for dynamically adjusting (e.g., hinted) default + // values. // // If override is true and the variable doesn't come from this root scope // or from the command line (i.e., it is inherited from the amalgamation), |