Constructor Arguments

Back to Deploying Contracts

Solidity constructors map to Neo's _deploy(data, update) entry point. The compiler automatically generates this entry point for contracts with constructors.

How It Works

1. The compiler emits a _deploy(data, update) method in the NEF.
2. On initial deployment (update = false), the deploy stub deserializes data and passes the values to your Solidity constructor logic.
3. On contract update (update = true), the constructor is skipped.

Passing Constructor Arguments

Neo-Express / CLI tooling: Pass a JSON array string as the -d flag:

# Constructor: constructor(uint256 initialValue)
$NEOXP contract deploy -i chain.neo-express -d '[7]' build/Counter.nef node1

# Constructor: constructor(uint256 amount, string name)
$NEOXP contract deploy -i chain.neo-express -d '[1000, "MyToken"]' build/Token.nef node1

Neo SDKs (C#, Python, JS): Pass a StackItem Array directly through the SDK's deploy API.

Contract-to-contract deployment: Use abi.encode(...) to produce StdLib.serialize bytes, which the deploy stub can also accept.

Manifest Requirements

Contracts with parameterized constructors require these permissions in the manifest:

• StdLib.jsonDeserialize
• StdLib.deserialize

The compiler adds these automatically. You can verify:

jq '.permissions' build/Counter.manifest.json

WARNING

If you use --deny-wildcard-methods and the compiler cannot narrow the StdLib permissions, compilation will fail. In that case, provide an explicit --manifest-permissions file that includes the required StdLib methods.