Delegate Call (Vyper Code Example)

When contract A delegates call to contract B, B's code will be executed inside contract A. This will update state variables and Ether balance inside contract A and not B.

Delegate call is commonly used to create an upgradable contract.

Here is the contract that we will delegate call to.

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TestDelegateCall.vy

# pragma version ^0.4.0

# State variables must be declared in the same order
# as contract making the call
x: public(uint256)
y: public(uint256)

@external
def update_x(x: uint256):
    # when this function is called with delegate call
    # this will update self.x inside the calling contract
    self.x = x + 1


@external
def update_y(y: uint256):
    self.y = y * y

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DelegateCall.vy

# pragma version ^0.4.0

x: public(uint256)
y: public(uint256)

@external
def update_x(to: address, x: uint256):
    raw_call(
        to,
        concat(
            method_id("update_x(uint256)"),
            convert(x, bytes32)
        ),
        is_delegate_call=True
    )

@external
def update_y(to: address, y: uint256):
    raw_call(
        to,
        concat(
            method_id("update_y(uint256)"),
            convert(y, bytes32)
        ),
        is_delegate_call=True
    )

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