Proposal

Additional option forexplicit-function-return-type ignores all but the final returned function when multiple fat-arrows appear in a function expression before a shared body.

{"rules": {"@typescript-eslint/explicit-function-return-type": ["error",      {"allowCurrying":true      }    ]  }}

Purpose

In functional programming, currying is a common pattern. With this pattern a function taking multiple parameters is instead modeled as a unary (1-parameter) function that returns a unary function that returns a unary function, .etc. With arrow functions, you can express this quite elegantly, but the intermediate return types are (usually) not of meaningful importance.

Example

Good: Explicit return given for last function returned by expression.

constfoo=(bar:string)=>(baz:string)=>(buz:string)=>(biz:string) :string=>`${bar}${baz}${buz}${biz}`constfiz=foo('bar')('baz')('buz')('biz')

Bad: Applied all parameters, but still failed to express a return type.

constbadFoo=(bar:string)=>(baz:string)=>(buz:string)=>(biz:string)=>`${bar}${baz}${buz}${biz}`

Note that in the example, there are technically 4 different functions in thefoo expression. But from a conceptual level, you can think of it as 1 function that must be called 4 times to apply all the parameters.

The type offoo( 'bar' ) is "foo with the first parameter fixed as'bar'". Trying to express that explicitly through the type system is a painful exercise in meaningless verbosity.

However, onceall the parameters are given, it still makes sense to enforce an explicit return type for the final returned value.