Ledger LandISSUE #36 of 90

erc-20 · the fungible token standard

BlockyVSDouble-Spend Dan

Blocky saysERC-20 is the standard interface for fungible tokens — interchangeable units like a currency.

ERC-20 defines a common set of functions (transfer, balanceOf, approve, allowance) so any wallet, exchange, or contract can handle any token the same way. "Fungible" means each unit is identical and interchangeable (1 USDC = 1 USDC). The standard is why thousands of tokens just work across the ecosystem — interoperability through a shared interface.

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Standard interface for fungible tokens
transfer/balanceOf/approve/allowance
Fungible = identical, interchangeable units
Interoperability across wallets/exchanges

Double-Spend Dan attacks — common mistakes

Assuming all tokens implement it perfectly
Forgetting approve+transferFrom for contract spends
Ignoring decimals when displaying balances

Boss battleName the two-step approve/transferFrom flow and why it exists.

Example code

<!doctype html><html><head><meta charset="utf-8"></head>
<body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre>ERC-20: transfer · balanceOf · approve · allowance
fungible: 1 unit == any other unit
shared interface → works everywhere</pre></body></html>

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