[exec.opstate.start]

# 33 Execution control library [[exec]](./#exec)

## 33.8 Operation states [[exec.opstate]](exec.opstate#start)

### 33.8.2 execution​::​start [exec.opstate.start]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1306)

The name start denotes a customization point object
that starts ([[exec.async.ops]](exec.async.ops "33.3 Asynchronous operations"))
the asynchronous operation associated with the operation state object[.](#1.sentence-1)

For a subexpression op,
the expression start(op) is ill-formed
if op is an rvalue[.](#1.sentence-2)

Otherwise, it is expression-equivalent to*MANDATE-NOTHROW*(op.start())[.](#1.sentence-3)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1316)

If op.start() does not start ([[exec.async.ops]](exec.async.ops "33.3 Asynchronous operations"))
the asynchronous operation associated with the operation state op,
the behavior of calling start(op) is undefined[.](#2.sentence-1)