https://github.com/eclipse/eclipse-collections/eclipse-collections-api: Eclipse Collections is a collections framework for Java. It has JDK-compatible List, Set and Map implementations with a rich API and set of utility classes that work with any JDK compatible Collections, Arrays, Maps or Strings. The iteration protocol was inspired by the Smalltalk collection framework.
  • Craig P. Motlin
  • Donald Raab
  • Mohammad A. Rezaei
  • Hiroshi Ito
  • Nikhil J. Nanivadekar
  • Sirisha Pratha 
public interface org.eclipse.collections.api.block.function.Function0<R> extends java.util.function.Supplier<R>, java.io.Serializable
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: org.eclipse.collections.api.block.function.Function0
  super_class: java.lang.Object
{
  public abstract R value();
    descriptor: ()Ljava/lang/Object;
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    Signature: ()TR;

  public R get();
    descriptor: ()Ljava/lang/Object;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // org.eclipse.collections.api.block.function.Function0 this
         0: .line 29
            aload 0 /* this */
            invokeinterface org.eclipse.collections.api.block.function.Function0.value:()Ljava/lang/Object;
            areturn
        end local 0 // org.eclipse.collections.api.block.function.Function0 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lorg/eclipse/collections/api/block/function/Function0<TR;>;
    Signature: ()TR;
}
Signature: <R:Ljava/lang/Object;>Ljava/lang/Object;Ljava/util/function/Supplier<TR;>;Ljava/io/Serializable;
SourceFile: "Function0.java"
    RuntimeVisibleAnnotations: 
      java.lang.FunctionalInterface()