Editing NOP (code) (section)

== Code ==
A function or a sequence of programming language statements is a NOP or null statement if it has no effect. Null statements may be required by the [[programming language syntax|syntax]] of some languages in certain contexts.

=== Ada ===
In [[Ada (programming language)|Ada]], the <code>null</code> statement serves as a NOP.<ref>[http://www.adaic.org/resources/add_content/standards/05aarm/html/AA-5-1.html#S0134 Ada Reference Manual &mdash; null statements]. "The execution of a null_statement has no effect."</ref> As the syntax forbids that control statements or functions be empty, the <code>null</code> statement must be used to specify that no action is required. (Thus, if the programmer forgets to write a sequence of statements, the program will fail to compile.)

=== C and derivatives ===
The simplest NOP statement in C is the ''null statement'', which is just a semi-colon in a context requiring a statement.

Most C compilers generate no code for null statements, which has historical and performance reasons. 
   ;
An empty block (compound statement) is also a NOP, and may be more legible, but will still have no code generated for it by the compiler.
   {}
In some cases, such as the body of a function, a block must be used, but this can be empty. In C, statements cannot be empty—simple statements must end with a <code>;</code> (semicolon) while compound statements are enclosed in <code>{}</code> (braces), which does not itself need a following semicolon. Thus in contexts where a statement is grammatically required, some such null statement can be used.

The null statement is useless by itself, but it can have a syntactic use in a wider context, e.g., within the context of a loop:
<syntaxhighlight lang="c">
  while (getchar() != '\n') {}
</syntaxhighlight>
alternatively,
<syntaxhighlight lang="c">

  while (getchar() != '\n')
      ;
</syntaxhighlight>
or more tersely:
<syntaxhighlight lang="c">

  while (getchar() != '\n');
</syntaxhighlight>
(note that the last form may be confusing, and as such generates a warning with some compilers or compiler options, as semicolon usually indicates an end of function call instruction when placed after a parenthesis on the end of line).

The above code continues calling the function <code>getchar()</code> until it returns a <code>\n</code> (newline) character, essentially fast-forwarding the current reading location of standard input to the beginning of next line.

=== Fortran ===
In [[Fortran]], the <code>CONTINUE</code> statement is used in some contexts such as the last statement in a DO loop, although it can be used anywhere, and does not have any functionality.

=== JavaScript ===
The [[JavaScript]] language does not have a built-in NOP statement. Many implementations are possible:
* Use the <code>;</code> ''empty statement''<ref>MDN JavaScript reference – [https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/Empty empty statement]. "The empty statement is a semicolon (<code>;</code>) indicating that no statement will be executed, even if JavaScript syntax requires one."</ref> or the <code>{}</code> empty ''block statement'' the same way as in the [[NOP (code)#C_and_derivatives|C and derivatives]] examples;
* Use the <code>undefined</code> or the <code>null</code> expression as a complete statement (an ''expression statement'') when the previous methods are not allowed by the syntax.
Alternatives, in situations where a function is required, are:
* Use the <code>Function.prototype()</code> built-in function, that accepts any arguments and returns <code>undefined</code>;<ref>ECMAScript Language Specification – Edition 5.1 – [https://www.ecma-international.org/ecma-262/5.1/#sec-15.3.4 Properties of the Function Prototype Object]</ref>
* Use a NOP function available in a third-party library —see below;
* Define a custom NOP function, as in the following example (using the [[ES6]] arrow function syntax):
<syntaxhighlight lang="javascript">const noop = () => {};</syntaxhighlight>

==== AngularJS ====
The [[AngularJS]] framework provides [https://docs.angularjs.org/api/ng/function/angular.noop angular.noop] function that performs no operations.

==== jQuery ====
The [[jQuery]] library provides a function <code>jQuery.noop()</code>, which does nothing.<ref>[http://api.jquery.com/jquery.noop/ jQuery.noop()] from jQuery API documentation</ref>

==== Lodash ====
The [[Lodash]] library provides a function <code>_.noop()</code>, which returns undefined and does nothing.<ref>{{Cite web|url=https://lodash.com/docs/#noop|title=Lodash Documentation|website=lodash.com|language=en|access-date=2017-12-15}}</ref>

=== Pascal ===
As with C, the ; used by itself can be used as a null statement in [[Pascal (programming language)|Pascal]]. In fact, due to the specification of the language, in a BEGIN / END block, the semicolon is optional before the END statement, thus a semicolon used there is superfluous. 

Also, a block consisting of <code> BEGIN END;</code> may be used as a placeholder to indicate no action, even if placed inside another BEGIN / END block.

=== Python ===
The [[Python (programming language)|Python]] programming language has a [[Python (programming language)#Statements and control flow|<code>pass</code> statement]] which has no effect when executed and thus serves as a NOP. It is primarily used to ensure correct syntax due to Python's [[off-side rule|indentation-sensitive syntax]]; for example the syntax for definition of a [[class (computer programming)|class]] requires an indented block with the class logic, which has to be expressed as <code>pass</code> when it should be empty.

=== Shell scripting (bash, zsh, etc.) ===
The '<code>:</code>' [colon] command is a shell builtin that has similar effect to a "NOP" (a do-nothing operation). It is not technically an NOP, as it changes the special parameter $? (exit status of last command) to 0. It may be considered a synonym for the shell builtin 'true', and its exit status is true (0).<ref>[http://tldp.org/LDP/abs/html/special-chars.html Advanced Bash-Scripting Guide > Chapter 3. Special Characters]</ref><ref>bash manpage > SHELL BUILTIN COMMANDS</ref><ref>zsh manpage (zshbuiltins) > SHELL BUILTIN COMMANDS</ref>

=== TeX macro language (ConTeXt, LaTeX, etc.) ===
The [[TeX]] typographical system's macro language has the <code>\relax</code> command.<ref>{{cite book |last1=Bausum |first1=David |title=TeX Reference Manual |date=2002 |publisher=Kluwer Academic Publishers |url=https://www.tug.org/utilities/plain/cseq.html#relax-rp |access-date=1 April 2020 |chapter=TeX Primitive Control Sequences |quote=According to The TeXbook, 'TeX does nothing' when it encounters <code>\relax</code>. Actually, <code>\relax</code> may tell TeX, 'This is the end of what you've been doing'.}}</ref> It does nothing by itself, but may be used to prevent the immediately preceding command from parsing any subsequent tokens.<ref>TeX wikibook – [https://en.wikibooks.org/wiki/TeX/relax relax]</ref>