Units and Globally Available Variables in Solidity 0.8.20

Ether Units

Literals in Solidity can include suffixes like wei, gwei, or ether to specify Ethereum denominations. Unsuffixed numbers default to wei.

Example:

assert(1 wei == 1);
assert(1 gwei == 1e9);
assert(1 ether == 1e18);

Note: Suffixes act as multipliers (e.g., 1 ether = 1e18 wei).

👉 Learn more about Ethereum units

Time Units

Time suffixes (seconds, minutes, hours, days, weeks) convert literals into seconds-based values:

• 1 minutes = 60 seconds
• 1 hours = 3600 seconds
• 1 weeks = 604800 seconds

Warning: Avoid using these for calendar calculations due to unpredictable leap seconds.

Special Variables and Functions

Block and Transaction Properties

• block.timestamp: Current block timestamp (seconds since Unix epoch).
• block.number: Current block height.
• msg.sender: Address of the caller.
• msg.value: Wei sent with the call.

Caution: block.timestamp and blockhash are miner-influenced and unsuitable for randomness.

ABI Encoding/Decoding

• abi.encode(...): Encodes arguments for external calls.
• abi.decode(...): Decodes ABI-encoded data.

Error Handling

• assert(bool condition): Reverts on internal errors (e.g., overflow).
• require(bool condition, string message): Reverts with a message for invalid inputs.

Cryptographic Functions

• keccak256(bytes): Computes Keccak-256 hash.
• ecrecover(bytes32 hash, ...): Recovers signer address from signatures.

👉 Explore Solidity security practices

Type Information

Use type(X) to inspect:

• type(C).creationCode: Bytecode for contract C deployment.
• type(uint).min/max: Min/max values for integer types.

Reserved Keywords

Future syntax may include: after, let, static, etc.

FAQ

Why avoid block.timestamp for randomness?

Miners can marginally influence timestamps, making them predictable.

How does abi.encodePacked differ from abi.encode?

encodePacked tightly packs arguments (may lead to hash collisions).

What replaces selfdestruct?

As of EIP-6049, selfdestruct is deprecated; redesign contracts to avoid it.

How to handle leap seconds in time calculations?

Use oracle services for precise calendar computations.