# Clang 15 documentation

## HLSL Resource Types

## Introduction

HLSL Resources are runtime-bound data that is provided as input, output or both to shader programs written in HLSL. Resource Types in HLSL provide key user abstractions for reading and writing resource data.

## Implementation Details

In Clang resource types are forward declared by the `HLSLExternalSemaSource` on initialization. They are then lazily completed when `requiresCompleteType` is called later in Sema.

Resource types are templated class declarations. The template parameter specifies the expected return type of resource loads, and the expected parameter type for stores.

In Clang’s AST and code generation, resource types are classes that store a pointer of the template parameter type. The pointer is populated from a call to `__builtin_hlsl_create_handle`, and treated as a pointer to an array of typed data through until lowering in the backend.

Resource types are annotated with the `HLSLResource` attribute, which drives code generation for resource binding metadata. The `hlsl` metadata nodes are transformed in the backend to the binding information expected by the target runtime.