关于erlang:apply/2/3

最新推荐文章于 2024-01-29 21:41:06 发布

最新推荐文章于 2024-01-29 21:41:06 发布 · 696 阅读

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本文探讨了Erlang中apply函数的工作原理及其在编译时如何被优化。通过内置函数(BIF)实现，实际调用过程由虚拟机直接处理而非通过Erlang代码。此外，还对比了Smalltalk中的类似机制。

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 57 apply(Fun, Args) ->
 58     apply(Fun,Args).                        
 59 
 60 apply(Mod, Name, Args) ->
 61     apply(Mod, Name, Args).

上面代码是erlang.erl文件里看到的。这里aplly/3方法里面又调用一次apply/3 请问是什么意思

老大: 在虚拟机里面实现的
langzhe: 谢谢
erlang.erl代码编译的时候进行了特殊编译？所以再调用时候不会默认调用erlang:apply/3?
老大: 恩

需要进一步看看是怎么编译的？

来自http://erlang.2086793.n4.nabble.com/Erlang-about-quot-apply-quot-function-in-the-erlang-erl-td3528347.html#a3531504的部分解释

apply is a built in function (BIF). It is implemented in C, not Erlang.

>
> apply is a built in function (BIF). It is implemented in C, not Erlang.
Does it work in a similar manner to that of Smalltalks, or differently?

In Smalltalks, `Boolean ifTrue: aBlock ifFalse: aBlock` literal forms
are usually compiled to call into native code directly, so the
implementation of this message in Smalltalk code in Smalltalk VMs looks
like this:

ifTrue:trueBlock ifFalse:falseBlock
^self ifTrue:[ trueBlock call ] ifFalse: [ falseBlock call ]

which looks like it would not work, but when the form
`var ifTrue:aBlockLiteral ifFalse:aBlockLiteral` is encountered the
Smalltalk compiler takes over and replaces this with native code. So the
Smalltalk implementation is only ever hit for non-literal sends (either
non-literal blocks, or usage of selectors), and its only role is to
redirect execution to the native version.

Is the purpose (and behavior) of the pure version of erlang:apply
similar?

－－－－－－－－－－引用Richard

It's a fairly common "bootstrapping" sort of thing.
Presumably
- when the compiler sees apply/2 or apply/3 in an expression
it generates special in-line code
- there needs to be a "real" function definition so that it
can be called indirectly itself, discoverable in the
module exports, traced if calls arrive that way in the
debugger, &c

apply的调用在beam加载的时候vm会调整相关的指令，实际上是在vm的opcode里面执行的。
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