Rvalue

As explained in Learn C++ by Example

An rvalue is an expression category representing a value that is generally suitable for moving or binding to an rvalue reference.

An rvalue is an expression category for a value that is usually temporary and suitable for moving. Unlike a named lvalue, it has no lasting name; using it can avoid copying data. section 2.2.3

Recognize rvalues through their role in container operations:

• A literal such as 42 is an rvalue, while a named variable such as x is an lvalue. section 2.2.3
• A temporary vector returned by get_next_row can bind to push_back(T&&) and be moved instead of copied. section 2.2.3
• emplace_back can construct the container element directly from the temporary. section 2.2.3

Moving temporary triangle rows

generate_triangle builds each row with get_next_row(triangle.back()) and passes that temporary directly to triangle.push_back, avoiding a separate copy. section 2.2.3

Figure 2.4 A move-constructed vector can steal the rvalue’s elements.

A move-constructed vector can take ownership of an rvalue's elements rather than duplicating them. section 2.2.3

How Learn C++ by Example covers it

How deep it goes

Defines rvalues through lvalue contrast, then explains references, move construction, and emplacement; defers full value-category details.

Examples

Demonstrates temporary vectors in triangle generation, push_back overloads, move construction, and vector storage diagrams.

What it assumes

Builds from named variables and literals, then introduces temporary vectors without requiring full value-category coverage.

What you can do after

Apply rvalues through push_back, emplace_back, and std::move to avoid copying temporary objects.

How it connects

Connects rvalues with lvalues, rvalue references, move semantics, move constructors, perfect forwarding, push_back, emplace_back, and std::move.

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Related concepts

• std::moveproduced by · std::move is a C++ standard-library function template that casts an expression to an rvalue reference, enabling move operations.
• is_move_constructiblemeasured by · is_move_constructible is a C++ type trait that determines whether a type can be constructed from an rvalue of the same type.
• rvalue referenceconfigured by · An rvalue reference is a C++ reference type, written with &&, that binds to rvalues, including temporary objects, and supports moving resources from them.
• lvaluecontrasts with · An lvalue is an expression that designates an identifiable object or storage location and can serve as an assignment target when the language permits.

This explainer was generated by Manning's knowledge graph from the text of Learn C++ by Example. The section links point to the parts of the book it draws on.