Function side effects will cause unnecessary trouble to programming, bring very difficult to find errors to the program, and reduce the readability of the program. Strict functional languages require that functions must have no side effects.
Several concepts related to side effects of functions, Pure Function, Impure Function, Referential Transparent.
Pure Function (Pure Function)
The input and output data streams are all explicit. Explicit means that there is only one unique channel for functions to exchange data with the outside world - parameters and return values. All input information received by a function from outside the function is passed into the function through parameters. All information output from the function outside the function is passed to the outside of the function through the return value.
Non-pure function ( Impure Function )
On the contrary. Implicit means that functions exchange data with the outside world through channels other than parameters and return values. For example, reading/modifying global variables is called exchanging data with the outside world in an implicit way.
Referential Transparent
The concept of citing transparency is related to and is affected by the side effects of functions. If two identical value expressions in a program can be replaced with each other anywhere in the program without affecting the program's actions, the program has reference transparency. Its advantage is that it is easier to understand and less obscure than the semantics of non-referenced transparent languages. Pure functional languages have no variables, so they all have reference transparency.
The following example illustrates the combination of citation transparency and function side effects
result1 = (fun(a) + b) / (fun(a) -c);
temp = fun(a);
result2 = (temp + b) / (temp -c);
If the function has no side effects, then result1 and result2 will be equivalent. However, if fun has side effects, such as adding 1 to b or c, then result1 and result2 will not be equal. Therefore, side effects violate citation transparency.
In JavaScript, functions are introduced. But obviously functions in JS can access and modify global variables (or define variables outside the function), as follows
var a = 5;
function fun(){
a = 10;
}
fun(); // a becomes 10
In JS, if you want to ensure that the function has no side effects, you can only rely on the habits of programmers, that is,
1. Function entry uses parameter operations without modifying it
2. Do not modify variables outside the function, such as global variables
3. The operation result is returned to the external (export) through the function
Several concepts related to side effects of functions, Pure Function, Impure Function, Referential Transparent.
Pure Function (Pure Function)
The input and output data streams are all explicit. Explicit means that there is only one unique channel for functions to exchange data with the outside world - parameters and return values. All input information received by a function from outside the function is passed into the function through parameters. All information output from the function outside the function is passed to the outside of the function through the return value.
Non-pure function ( Impure Function )
On the contrary. Implicit means that functions exchange data with the outside world through channels other than parameters and return values. For example, reading/modifying global variables is called exchanging data with the outside world in an implicit way.
Referential Transparent
The concept of citing transparency is related to and is affected by the side effects of functions. If two identical value expressions in a program can be replaced with each other anywhere in the program without affecting the program's actions, the program has reference transparency. Its advantage is that it is easier to understand and less obscure than the semantics of non-referenced transparent languages. Pure functional languages have no variables, so they all have reference transparency.
The following example illustrates the combination of citation transparency and function side effects
Copy the codeThe code is as follows:
result1 = (fun(a) + b) / (fun(a) -c);
temp = fun(a);
result2 = (temp + b) / (temp -c);
If the function has no side effects, then result1 and result2 will be equivalent. However, if fun has side effects, such as adding 1 to b or c, then result1 and result2 will not be equal. Therefore, side effects violate citation transparency.
In JavaScript, functions are introduced. But obviously functions in JS can access and modify global variables (or define variables outside the function), as follows
Copy the codeThe code is as follows:
var a = 5;
function fun(){
a = 10;
}
fun(); // a becomes 10
In JS, if you want to ensure that the function has no side effects, you can only rely on the habits of programmers, that is,
1. Function entry uses parameter operations without modifying it
2. Do not modify variables outside the function, such as global variables
3. The operation result is returned to the external (export) through the function