Rule: `option_map_or_else_none_and_some`

[tvolk131]

What it does

Very similar to the option_map_or_none rule.

When calling map_or_else() on an Option<T> and the following two conditions are met:

• The default parameter is a lambda that always returns None
• The f parameter is a lambda that always returns Some

This is effectively a more verbose way of doing what Option::map() does.

Advantage

Code is shorter, more expressive, and more concise.

Drawbacks

Given that this rule is only applicable within such narrow constraints, I don't think there is any downside.

Example

Some(1).map_or_else(|| None, |num| Some(num + 1))

Could both be written as:

Some(1).map(|num| num + 1)

[nyurik]

while similar to option_map_or_none, this lint would need to modify lambda code, which I would think is slightly trickier:

• |v| { let i = foo(); Some(i + v) }
• |v| if v > 10 { Some(v+1) } else { Some(v-1) }
• |v| match v { 1 => Some(1), _ => Some(v+1) }
• a combination of the above

In other words, there would need to be code evaluating every code path inside the lambda to check that every one either returns Some(...) or ! (i.e. panics)

[tvolk131]

this lint would need to modify lambda code

Good point! I was thinking solely of lambdas that immediately return None or Some, but the examples you listed would be nice to tackle too. I imagine the simple case could be done first, and the cases you mentioned could be added later.