Kotlin 可以动态为对象绑定一个额外对象吗？

Question

我有一个方法，每次都必须传入一个固定的对象paint,因为这个函数会被频繁调用，所以我不能在内联函数中创建对象。
inlinefunCanvas.drawPoint(
point:PointF,
paint:Paint){
drawPoint(point.x,point.y,paint)
}
但是我很多地方都会调用这个方法。
//(Canvas.apply(..,..))
drawPoint(pointA,pointPaint)
drawPoint(pointB,pointPaint)
drawPoint(pointC,pointPaint)
drawPoint(pointD,pointPaint)
可以看到每次都会传入一个pointPaint对象。所以我在想有没有类似这样一个功能
//(Canvas.apply(..,..))
bind(pointPaint)
drawPoint(pointA)
drawPoint(pointB)
drawPoint(pointC)
drawPoint(pointD)

Answer 1

完美符合你要求的方式肯定是没有的，因为bind函数不可能改变另一个函数内部的局部变量。折中的方式也有很多，比如定义一个包级属性：vardrawPaint:Paint?=null然后原来的函数改为：inlinefunCanvas.drawPoint(point:PointF,paint:Paint){paint?.let{drawPoint(point.x,point.y,it)}}方便使用还可以再定义一个函数来确保drawPaint能被准确的赋值和释放：funbindPaint(paint:Paint,action:()->Unit){drawPaint=paintaction()drawPaint=null}这样使用时就是：//Canvas().apply{bindPaint(somePaint){drawPoint(x,y)}还有一种方式是定义一个包装类，并在其中定义一个包含带接收者Lambda表达式的参数的函数（接收者为Canvas），然后将扩展函数定义到这个类中：classPointPainter(privatevalpaint:Paint){funCanvas.drawPoint(rect:RectF){drawPoint(rect.x,rect.y,paint)}}然后定义含有接收者为这个包装对象Lambda参数的函数：funbindPointPainter(paint:Paint,drawAction:PointPainter.()->Unit){PointPainter(paint).drawAction()}这样用时更方便一些：//incanvas.applyblockbindPointPainter(somePaint){drawPoint(rect1)drawPoint(rect2)//...}

Answer 2

funtest(){Canvas().bindPaintDrawPoints(Paint())(arrayOf(PointF(1f,2f),PointF(2f,2f),PointF(3f,2f),PointF(4f,2f)))}funCanvas.bindPaintDrawPoints(paint:Paint):(Array)->Unit{return{drawPoints(paint,it)}}funCanvas.drawPoints(paint:Paint,points:Array){for(pinpoints){this.drawPoint(p.x,p.y,paint)}}