(make.info)Static versus Implicit


Static Pattern Rules versus Implicit Rules
------------------------------------------

   A static pattern rule has much in common with an implicit rule
defined as a pattern rule (*note Defining and Redefining Pattern Rules:
Pattern Rules.).  Both have a pattern for the target and patterns for
constructing the names of prerequisites.  The difference is in how
`make' decides _when_ the rule applies.

   An implicit rule _can_ apply to any target that matches its pattern,
but it _does_ apply only when the target has no commands otherwise
specified, and only when the prerequisites can be found.  If more than
one implicit rule appears applicable, only one applies; the choice
depends on the order of rules.

   By contrast, a static pattern rule applies to the precise list of
targets that you specify in the rule.  It cannot apply to any other
target and it invariably does apply to each of the targets specified.
If two conflicting rules apply, and both have commands, that's an error.

   The static pattern rule can be better than an implicit rule for these
reasons:

   * You may wish to override the usual implicit rule for a few files
     whose names cannot be categorized syntactically but can be given
     in an explicit list.

   * If you cannot be sure of the precise contents of the directories
     you are using, you may not be sure which other irrelevant files
     might lead `make' to use the wrong implicit rule.  The choice
     might depend on the order in which the implicit rule search is
     done.  With static pattern rules, there is no uncertainty: each
     rule applies to precisely the targets specified.


automatically generated by info2www version 1.2.2.9