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# MTLFunctionConstant

A constant that specializes the behavior of a shader.

```
class MTLFunctionConstant
```

## Overview

Don’t create an [`MTLFunctionConstant`](/documentation/Metal/MTLFunctionConstant) instance directly. Instead, the list of function constants for a function by querying the `functionConstants` property of an [`MTLFunction`](/documentation/Metal/MTLFunction) instance.

An [`MTLFunctionConstant`](/documentation/Metal/MTLFunctionConstant) instance should only be obtained from a nonspecialized function created with the [`makeFunction(name:)`](/documentation/Metal/MTLLibrary/makeFunction(name:)) method. You only need an [`MTLFunctionConstant`](/documentation/Metal/MTLFunctionConstant) instance if you don’t have sufficient information to create an [`MTLFunctionConstantValues`](/documentation/Metal/MTLFunctionConstantValues) instance used to create a specialized function with the [`makeFunction(name:constantValues:)`](/documentation/Metal/MTLLibrary/makeFunction(name:constantValues:)) or [`makeFunction(name:constantValues:completionHandler:)`](/documentation/Metal/MTLLibrary/makeFunction(name:constantValues:completionHandler:)) method.

## Topics

### Reading the function constant’s properties

[`name`](/documentation/Metal/MTLFunctionConstant/name)

The name of the function constant.

[`type`](/documentation/Metal/MTLFunctionConstant/type)

The data type of the function constant.

[`index`](/documentation/Metal/MTLFunctionConstant/index)

The index of the function constant.

[`required`](/documentation/Metal/MTLFunctionConstant/required)

A Boolean value indicating whether the function constant needs to be provided to specialize the function.


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