diff options
Diffstat (limited to 'doc/manual.cli')
| -rw-r--r-- | doc/manual.cli | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/doc/manual.cli b/doc/manual.cli index 93053e4..847691d 100644 --- a/doc/manual.cli +++ b/doc/manual.cli @@ -4966,6 +4966,32 @@ if! $defined(config.libhello.database) fail 'config.libhello.database must be specified' \ +\N|A configuration variable without a default value is omitted from +\c{config.build} unless the value is specified by the user. This semantics is +useful for values that are normally derived from other configuration values +but could also be specified by the user. If the value is derived, then we +don't want it saved in \c{config.build} since that would prevent it from +being re-derived if the configuration values it is based on are changed. +For example: + +\ +config [strings] config.hello.database + +assert ($size($config.hello.database) > 0) \ + 'database must be specified with config.hello.database' + +config [bool, config.report.variable=multi] config.hello.multi_database + +multi = ($defined(config.hello.multi_database) \ + ? $config.hello.multi_database \ + : $size(config.hello.database) > 1) + +assert ($multi || $size(config.hello.database) == 1) \ + 'one database can be specified if config.hello.multi_database=false' +\ + +| + If computing the default value is expensive or requires elaborate logic, then the handling of a configuration variable can be broken down into two steps along these lines: |