Glossary definition

Function selector

An EVM function selector is the first four bytes of the Keccak-256 hash of a function's canonical signature, used to dispatch external calls.

also: method selector, 4-byte selector · reviewed July 22, 2026

For transfer(address,uint256), the selector is derived from that exact name and parameter-type string. The selector prefixes ABI-encoded arguments in call data so a contract’s dispatcher can choose the intended external function.

Four bytes are not collision resistant. Different signatures can share a selector, which matters when a proxy and implementation expose separate interfaces or when dispatch is assembled manually. Compilers catch collisions inside one interface, but cross-contract composition still needs review. The Solidity ABI specification defines canonical signature encoding.

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