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 
public interface org.eclipse.collections.api.block.function.primitive.DoubleFunction<T> extends java.util.function.ToDoubleFunction<T>, 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.primitive.DoubleFunction
  super_class: java.lang.Object
{
  public abstract double doubleValueOf();
    descriptor: (Ljava/lang/Object;)D
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    Signature: (TT;)D
    MethodParameters:
          Name  Flags
      anObject  

  public double applyAsDouble();
    descriptor: (Ljava/lang/Object;)D
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // org.eclipse.collections.api.block.function.primitive.DoubleFunction this
        start local 1 // java.lang.Object value
         0: .line 31
            aload 0 /* this */
            aload 1 /* value */
            invokeinterface org.eclipse.collections.api.block.function.primitive.DoubleFunction.doubleValueOf:(Ljava/lang/Object;)D
            dreturn
        end local 1 // java.lang.Object value
        end local 0 // org.eclipse.collections.api.block.function.primitive.DoubleFunction this
      LocalVariableTable:
        Start  End  Slot   Name  Signature
            0    1     0   this  Lorg/eclipse/collections/api/block/function/primitive/DoubleFunction<TT;>;
            0    1     1  value  TT;
    Signature: (TT;)D
    MethodParameters:
       Name  Flags
      value  
}
Signature: <T:Ljava/lang/Object;>Ljava/lang/Object;Ljava/util/function/ToDoubleFunction<TT;>;Ljava/io/Serializable;
SourceFile: "DoubleFunction.java"
    RuntimeVisibleAnnotations: 
      java.lang.FunctionalInterface()