CODEWITHSUNDEEP
groovy
Paul
Paul

Reputation: 3058

In Groovy, can you get a method reference to a local or statically imported method without restating the class?

Ideally I'd like to be able to express the idea: "whatever would be called by foo() in the current position in the code, give me a method reference to foo".

Rationale: I'm working on some code that uses a lot of high-order functions and function composition. I'd like: a) it to be as terse as possible, and b) not to have to keep editing class names scattered around the code as I refactor and move functions between classes.

For example:

/* ---- foo.pkg1.Utils.groovy */
public final class Utils {

    private Utils() { /* as it's all static methods */ }

    static foo() { 42; }

}

/* ---- foo.pkg2.Client1.groovy */
import foo.pkg1.Utils

def f1 = Utils.&foo // <-- restates class (but works)
println f1()

/* ---- foo.pkg2.Client2.groovy */
import static foo.pkg1.Utils.*

def f2 = foo  // <-- No!
// "groovy.lang.MissingPropertyException: No such property: foo ..."
println f2() 

def f3 = &foo  // <-- No!
// "unexpected token: & at line: 17, column: 14"
println f3()

def f4 = this.&foo  // <-- Also no!
// "groovy.lang.MissingMethodException: No signature of method..."
println f4()

/* ---- foo.pkg2.Client3.groovy */
/* My best attempt ... but this only allows me to change which
   class 'u' refers too, not to create a method reference to
   whatever `foo()` would call at the same place in the code. */
import static Utils as u

def f5 = u.&foo
println f5()

Upvotes: 1

Views: 340

Answers (2)

Will
Will

Reputation: 14519

Slightly error-prone due to variable naming being bounded to with order, but it is something:

    class Util {
        static foo(arg) { "foo $arg" }
        static bar() { "bar" }
        static batman(fn) { fn("captain") }
    }

    def (foo, bar, batman) = Util.with { [it.&foo, it.&bar, it.&batman] }

    assert foo("eck") == "foo eck"

    assert batman(foo) == "foo captain"

Handling the script's own binding using reflection on Util class is also an option if you always use scripts.

Upvotes: 1

dmahapatro
dmahapatro

Reputation: 50245

You can have the MethodClosure defined as a private static property of the class Utils like:

import org.codehaus.groovy.runtime.MethodClosure

public final class Utils {
    private static final MethodClosure fooPointer = this.&foo
    private Utils() { }
    static foo() { 42 }
}

// Client
import static Utils.*
def f1 = fooPointer
println f1()

Do not know how will it be advantageous anyway.

Upvotes: 0

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