A Gant target is a binding of a closure to a name:
target(name: target-name) target-closure
the parameter of the call of the target function is a map that must have the key name, and may have other keys. Perhaps the most important other key is description:
target(name: target-name , description: target-description) target-closure
Giving a target a name and a description is such a common form that there is a short-cut for this:
target(target-name: target-description) target-closure
So for example:
can be written:
In this form, any legal Groovy string can be used as the target-name but if it a Groovy keyword then it must be explicitly a string (automatic stringification doesn’t work for Groovy keywords).
The target-description string is used as the string to output when executing “gant -p” (or “gant -T”) to discover the list of allowed command-line targets. If target-description is missing or is the empty string then the target will not appear in the target list - using the short-cut form of target, the descritpion string must always be present but it can be the empty string. Only targets with non-empty descriptions are treated as callable targets.
The target-closure can contain any legal Groovy code. An AntBuilder is pre- defined and is called ant, so calls can be made to any Ant task:
Calling Ant tasks in a Gant closure is so common that Gant automatically tries the ant object during function lookup. Hence the above can be written:
The usual rules associated with working with an AntBuilder in a Groovy script apply.
As each target labels a closure, targets can be called from other targets:
Target flob is called as part of target adob. This allows a lot of dependency information to be expressed. However, the calls are always made, there is no implicit checking whether a target has already been executed. Instead there is a method depends that can be used to handle the situation where a target should only be called if it has not been executed already in this run.
The depends method is an executable method so it can be called at any time in a target closure. This allows for a much more flexible expression of dependency than specifying dependencies as a property of the target (as is done in Ant for example).
In the above examples, the target name was always a string literal - Groovy ‘stringyfies’ the key of a map by default and that is what is happening here. Often, particularly when synthesizing targets programmatically (the huge benefit of Gant over Ant!), we want the name of the target to be constructed. No problem here, we can do things like:
Putting parentheses around the bit before the colon means that Groovy evaluates the expression and uses the result as the target name.
You might contemplate using GStrings in target names, and indeed descriptions, for example:
However, this is, in general, not a good thing to do. The reason is that GStrings are evaluated only on actual use and this means that if variable bindings have changed, the target name you thought you had is not the target name you actually have. There can be too much dynamism some times. So it is always wise to ensure that target names are fully evaluated at the point of target definition. There is no block to target synthesis, it just means don’t use GStrings as target names.