Why Can't We Use Non-Const References to Temporary Objects in C ?

Why Not Non-Const References to Temporary Objects?

In C , assigning temporary objects is permitted only to constant references. This restriction stems from the potential for unintended consequences when modifying temporary objects, as demonstrated in the following example:

void inc(int& x) { x += 1; }

int i = 0;
inc(i);

In this scenario, the temporary object returned by i is passed to the inc() function. However, modifying the temporary object does not affect i since the temporary object has already vanished by the time the function returns.

While preventing write access to temporary objects is crucial for avoiding such inconsistencies, it raises the question: why is read access allowed? If a temporary object ceases to exist after the statement, why is it permissible to read its contents?

The rationale behind allowing read access is to facilitate the use of data structures that rely on references to objects. For instance, a list may contain references to its elements. If elements were to disappear after each statement, such data structures would become impractical.

Allowing constant references to temporary objects ensures that they can be safely used in such scenarios without the risk of modifying their contents. This distinction between read and write access provides a balance between protecting data integrity and enabling efficient data manipulation.

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