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Run ABI examples in the interactive playground

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Overview

Selectors identify functions, events, and errors in Ethereum. Generated from human-readable signatures using keccak256 hashing.

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Function Selectors

Function selector: First 4 bytes of keccak256(signature) 
// transfer(address,uint256)
// Signature: "transfer(address,uint256)"
// Hash: keccak256("transfer(address,uint256)")
// Selector: 0xa9059cbb (first 4 bytes)

const selector = Abi.Function.getSelector(fn);
Canonical form: No spaces, canonical type names (e.g., uint256 not uint)

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Event Selectors

Event selector: Full 32 bytes of keccak256(signature) (topic0) 
// Transfer(address,address,uint256)
// Signature: "Transfer(address,address,uint256)"
// Hash: keccak256("Transfer(address,address,uint256)")
// Selector: 0xddf252ad... (full 32 bytes)

const selector = Abi.Event.getSelector(event);
Anonymous events: No topic0 (no selector), all parameters become topics

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Error Selectors

Error selector: First 4 bytes of keccak256(signature) (same as functions) 
// InsufficientBalance(uint256,uint256)
// Selector: First 4 bytes of keccak256(signature)

const selector = Abi.Error.getSelector(error);

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Signature Generation

Signatures represent function/event/error in canonical form. 
// Function: name(param1Type,param2Type)returns(returnType)
const sig = Abi.Function.getSignature(fn);
// "transfer(address,uint256)"

// Event: name(param1Type,param2Type)
const sig = Abi.Event.getSignature(event);
// "Transfer(address,address,uint256)"

// Error: name(param1Type,param2Type)
const sig = Abi.Error.getSignature(error);
// "InsufficientBalance(uint256,uint256)"

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Canonical Type Names

Types must use canonical names for correct selectors:
  • ✅ uint256, int256 (explicit size)
  • ❌ uint, int (implicit size - invalid)
  • ✅ bytes32 (fixed-size bytes)
  • ✅ bytes (dynamic bytes)
  • ✅ address (20 bytes)
  • ✅ bool (1 byte)

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Tuple Signatures

Tuples (structs) expand into signature: 
// struct Point { uint256 x; uint256 y; }
// function plot(Point p)
// Signature: "plot((uint256,uint256))"

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Array Signatures

Arrays include brackets in signature: 
// function batch(address[] recipients)
// Signature: "batch(address[])"

// function fixed(uint256[3] values)
// Signature: "fixed(uint256[3])"

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Selector Collisions

4-byte function selectors can collide (birthday paradox). ~77,000 functions → 50% collision chance. Event selectors (32 bytes) have negligible collision risk.

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Standard Selectors

Common function selectors:
  • 0xa9059cbb - transfer(address,uint256)
  • 0x23b872dd - transferFrom(address,address,uint256)
  • 0x095ea7b3 - approve(address,uint256)
  • 0x70a08231 - balanceOf(address)
Common event selectors:
  • 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef - Transfer(address,address,uint256)
  • 0x8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925 - Approval(address,address,uint256)

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Custom Hash Functions

Use factories for custom keccak256 implementations: 
import { GetSelector } from 'tevm/Abi/Function';

const getSelector = GetSelector(customKeccak256);
const selector = getSelector(fn);

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See Also