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This article mainly introduces how to apply the Perl closure, which has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, let the editor take you to understand it.

The basic concept of closure

Closures are blocks of code that can contain free (unbound) variables; these variables are not defined in this code block or any global context, but in the environment in which the code block is defined. the word "closure" comes from a combination of the block of code to be executed (the relevant variable reference is not released due to the existence of free variables) and the computational environment (scope) that provides binding for free variables. Varying degrees of support for closures can be found in languages such as Scheme, CommonLisp, Smalltalk, Groovy, JavaScript, Ruby, and Python.

Perl closure

Closure is a computer term that is precise but difficult to explain. In Perl, Perl closures are implemented in the form of anonymous functions with the ability to continuously refer to literal variables outside the scope of the function. These external literal variables magically retain their values (deep links) when the closure function was originally defined.

A Perl closure makes sense if one programming language allows a function to return another function (like Perl). It is important to note that some languages provide the functionality of anonymous functions but do not handle closures correctly; Python is an example. If you want to know more about closures, you are advised to look at this functional programming textbook. The language Scheme not only supports closures, but also encourages more use.

The following is a typical function that generates a function:

Subadd_function_generator {returnsub {shift+shift};} $add_sub=add_function_generator (); $sum=&$add_sub (4 sum 5); # $sum is now 9

The Perl closure is used like a function template, leaving some blanks that can be filled in later. The anonymous function returned by add_function_generator () is not technically a closure because it does not use any literal variables that are outside the scope of the function.

Compare the above example with the following make_adder () function, which returns an external literal variable in the anonymous function. This practice of naming an external function requires Perl to return an appropriate closure, so the value of that literal variable when the anonymous function is generated is locked into the closure.

Submake_adder {my$addpiece=shift; returnsub {shift+$addpiece};} $f1=make_adder (20); $f2=make_adder

In this way & $F1 ($n) will always be 20 plus the value you pass in $n, and & $f2 ($n) will always be 555 plus the value you pass in $n. The value of $addpiece is retained in the closure.

Perl closures are also commonly used in practical situations, such as when you want to pass some code into a function:

My$line

Timeout (30J sub {$line=})

If the code to be executed was passed in as a string, that is,'$line=', then the hypothetical function timeout () can no longer retrieve the value of the literal variable $list when it returns to the range in which the function was called.

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