Lazy.h

/*********************************************************************** Author: Zihan Chen (vczh) Licensed under https://github.com/vczh-libraries/License ***********************************************************************/

#ifndef VCZH_LAZY

#define VCZH_LAZY

#include "Pointer.h"

#include "Function.h"

namespace

{

/// <summary>A type representing a lazy evaluation.</summary>

/// <typeparam name="T">The type of the evaluation result.</typeparam>

template

typename

class

Lazy

public

Object

{

protected

class

Internal

{

public

Func

()>

evaluator

;

value

;

bool

evaluated

; };

Ptr

Internal

internalValue

;

public

/// <summary>Create an empty evaluation.</summary>

Lazy

() =

default

;

/// <summary>Create an evaluation using a function, which produces the evaluation result.</summary>

/// <param name="evaluator">The function.</param>

Lazy

(

const

Func

()>&

evaluator

) {

internalValue

new

Internal

;

internalValue

evaluated

false

;

internalValue

evaluator

; }

/// <summary>Create an evaluation with the immediate result.</summary>

/// <param name="value">The result.</param>0

Lazy

(

const

value

) {

internalValue

new

Internal

;

internalValue

evaluated

true

;

internalValue

value

; }

/// <summary>Create an evaluation by copying another one.</summary>

/// <param name="lazy">The evaluation to copy.</param>

Lazy

(

const

Lazy

lazy

) =

default

;

/// <summary>Create an evaluation by moving another one.</summary>

/// <param name="lazy">The evaluation to move.</param>

Lazy

(

Lazy

>&&

lazy

) =

default

;

Lazy

operator

(

const

Func

()>&

evaluator

) {

internalValue

new

Internal

;

internalValue

evaluated

false

;

internalValue

evaluator

;

return

this

; }

Lazy

operator

(

const

value

) {

internalValue

new

Internal

;

internalValue

evaluated

true

;

internalValue

value

;

return

this

; }

Lazy

operator

(

const

Lazy

lazy

) {

internalValue

lazy

internalValue

;

return

this

; }

/// <summary>Get the evaluation result. If the evaluation has not been performed, it will run the evaluation function and cache the result.</summary>

/// <returns>The evaluation result.</returns>

const

Value

()

const

{

internalValue

evaluated

) {

internalValue

evaluated

true

;

internalValue

value

internalValue

evaluator

(

);

internalValue

evaluator

Func

()>(); }

return

internalValue

value

; }

/// <summary>Test if it has already been evaluated or not.</summary>

/// <returns>Returns true if it has already been evaluated.</returns>

bool

IsEvaluated

()

const

{

return

internalValue

evaluated

; }

/// <summary>Test if it is an empty evaluation or not.</summary>

/// <returns>Returns true if it is not empty.</returns>

operator

bool

()

const

{

return

internalValue

; } }; }

#endif