Copy Elision in Modern C++

Copy Elision in Modern C++

Copy elision is an automatic C++ compiler optimization that “elides” (removes) various “copy” operations on objects. I guess “copy removal” just didn’t have the same ring to it?

Copy elision works in particular situations in the C++ language. These situations include:

• Class-type return statements — the main situation.
• throw expressions (and handlers)
• Coroutines

The effect of copy elision is to avoid a full object copy. Instead, the place where the new object is used simply refers to the old object, which would have been copied without this optimization.

Technically, there are other unusual situations, and there are two variants of copy elision:

• Removal of copying, or
• Downgrading copying to a move operation.

You don’t need to modify your code to get the benefits of copy elision. In fact, you also don’t need to turn the optimizer up to eleven. Copy elision is a normal part of the C++ standard.

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