groovy.transform

Annotation Type NamedVariant

@Incubating
 @Retention(value=SOURCE)
 @Target(value={METHOD,CONSTRUCTOR})
public @interface NamedVariant

Allows construction of a named-arg equivalent method or constructor. The method or constructor will have at least a first argument of type Map and may have more arguments. As such, it can be called using Groovy's named-arg syntax. The original method/constructor is retained and is called by the generated method/constructor. One benefit of this approach is the potential for improved type checking. The annotated "tuple" method/constructor can be type rich and will be checked as such during normal compilation. The generated method/constructor using the map argument will be named-argument friendly but the map also hides type information. The generated method however contains no business logic so the chance of errors is minimal. Any arguments identified as named arguments will be supplied as part of the map. Any additional arguments are supplied in the normal tuple style. Named parameters are identified in one of three ways:

1. Use one or more @NamedParam annotations to explicitly identify such parameters
2. Use one or more @NamedDelegate annotations to explicitly identify such parameters as delegate parameters
3. If no parameters with @NamedParam or @NamedDelegate annotations are found then:
   • If autoDelegate is false (the default), all parameters are treated as if they were named parameters
   • If autoDelegate is true, the first parameters is treated as if it was a delegate parameter

You can also mix and match the @NamedParam and @NamedDelegate annotations. Named arguments will be supplied via the map with their property name (configurable via annotation attributes within @NamedParam) being the key and value being the argument value. For named delegates, any properties of the delegate can become map keys. Duplicate keys across delegate properties or named parameters are not allowed. The type of delegate parameters must be compatible with Groovy's as cast operation from a Map. Here is an example using implicit named parameters.

 import groovy.transform.*

 @NamedVariant
 int makeSense(int dollars, int cents) {
     100 * dollars + cents
 }

 assert makeSense(dollars: 2, cents: 50) == 250
 

Here is an example using a delegate parameter.

 import groovy.transform.*

 @ToString(includeNames=true)
 class Color {
     Integer r, g, b
 }

 @NamedVariant
 String foo(@NamedDelegate Color shade) {
     shade
 }

 def result = foo(g: 12, b: 42, r: 12)
 assert result.toString() == 'Color(r:12, g:12, b:42)'
 

You could also explicitly annotate the shade argument with the @NamedDelegate annotation if you wanted. The generated method will be something like this:

 String foo(Map args) {
     return foo(args as Color)
 }
 

The generated method/constructor retains the visibility and return type of the original method/constructor but the VisibilityOptions annotation can be added to customize the visibility. You could have the annotated method/constructor private for instance but have the generated one be public.

Since:

2.5.0

See Also:

VisibilityOptions, NamedParam, NamedDelegate

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
boolean	autoDelegate If true, add an implicit @NamedDelegate to the first parameter if no @NamedDelegate or @NamedParam annotations are found on any parameter.
String	visibilityId If specified, must match the optional "id" attribute in an applicable VisibilityOptions annotation.

Element Detail

visibilityId

public abstract String visibilityId

If specified, must match the optional "id" attribute in an applicable VisibilityOptions annotation.

Default:

"<DummyUndefinedMarkerString-DoNotUse>"

autoDelegate

public abstract boolean autoDelegate

If true, add an implicit @NamedDelegate to the first parameter if no @NamedDelegate or @NamedParam annotations are found on any parameter.

Since:

2.5.3

Default:

false