more_on_functions.md

Chapter 10: More on Functions

In this chapter, we're going to learn about function return values, and optional function decorators.

Return Values

To return a value from a function, the declaration looks like this:

nameToAge: HashMap[String[64], uint256]

@external
def getAge(name: String[64]) -> uint256:
    return self.nameToAge[name]

The above getAge function returns a uint256 which is represented by the symbol -> followed by the return type uint256.

Function decorators

In a previous chapter, we explored 2 of the function decorators: @internal and @external.

There are a few more optional function decorators:

Decorator	Description
@pure	Function does not read contract state or environment variables
@view	Function does not alter contract state, but may read contract state
@payable	Function is able to receive Ether
@nonreentrant(<unique_key>)	Function cannot be called back into during an external call

Following the above example, we can add @view function decorator on the getAge function as it reads the contract state (storage variable) but does not alter it.

nameToAge: HashMap[String[64], uint256]

@view
@external
def getAge(name: String[64]) -> uint256:
    return self.nameToAge[name]

Put it to the test

We want to create an internal function which does not read or alter the contract state or environment variables (meaning a pure function) which returns a uint256.

1. Create an function named _generateRandomDNA with internal and pure function decorators.
2. The function should accept an input parameter: _name of type String[32].
3. The function returns a uint256 type.
4. Use the pass keyword to define an empty function body.

** Template **

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** Solution **

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** Previous Chapter Solution **

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