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layout: stdlib-reference
---
# attribute [nonmutating]
## Description
Marks a function or a property and subscript accessor as non-mutating. A non-mutating function receives the implicit this parameter
as an in parameter, so mutations to members accessed from this argument will be prohibited by the compiler.
## Signature
[nonmutating]
## Remarks
Member functions of a type are non-mutating by default, so this attribute is not necessary in most cases.
However, the set accessor of a property or subscript is mutating by default, and you can use [nonmutating] to mark it as non-mutating.
For example:
```csharp
struct S
{
int* ptr_x;
property x : int
{
get { return *ptr_x; }
[nonmutating]
set { *ptr_x = value; }
}
}
uniform S s; // `s` is not mutable.
void test() { s.x = 1; } // OK, because the `set` accessor is non-mutating.
```
In the above example, the property x reads and writes to a memory location pointed to by ptr_x. Therefore, the set accessor is not actually
modifying any field of S, and does not need to take this as an inout parameter. Using [nonmutating] here on the set accessor will allow
it to be called with a non-mutating value of S.
## See also
[mutating].