Understand lifetime extension limits for references

Binding a temporary directly to const T& extends the temporary’s lifetime. This is useful, but easy to misuse when subobjects are involved.

const Object& a = getObject();                   // Lifetime extension if getObject() returns by value
const Object& b = CreateParent().object;         // Lifetime extension for Parent temporary (and therefore its member)
const Object& c = CreateParent().getObject();    // WARNING: usually no lifetime extension of the referenced subobject

In the third case, getObject() may return a reference to a subobject owned by a temporary parent. Although direct member access can keep that temporary alive (second case), this does not generally apply through a method that returns a reference. The parent is destroyed at the end of the full expression, so c may dangle.

Tip

Enable AddressSanitizer (-fsanitize=address) in CI and local testing builds. It will produce a stack-use-after-scope error for the dangling reference in this situation.

Prefer safer designs

• Return by value when practical
• Avoid exposing references to subobjects of temporaries
• Keep owner lifetime explicit at call sites

Related

• Prefer returning by value over returning by const reference for value objects
• Avoid storing std-span as class members
• Tip of the Week #107: Reference Lifetime Extension Titus Winters, abseil.io
• Chained Functions Break Reference Lifetime Extension cpptruths.blogspot.com