[Pitch] Inferred Modified Initialisers for Structs

Evolution Pitches
1

Currently, if you want to modify a struct's default memberwise initialiser you have to write one out manually/auto-generate one via the IDE.

struct ImAStruct {
    let aVariable: String
    
    // This is inferred and doesn't need writing manually
    init(aVariable: String) {
        self.aVariable = lovelyVariable
    }
}

For example:

struct ImAStruct {
    let aVariable: String

    // This cannot be inferred due to the modification
    init(aVariable: String) {
        self.aVariable = aVariable
        
        if aVariable.contains("something") {
            print("Has something")
        }
    }
}

Could be something such as:

struct ImAStruct {
    let aVariable: String
    
    inferred init {
        if aVariable.contains("something") {
            print("Has something")
        }
    }
}

In an inferred init, you wouldn't need to manually assign variables/constants. This is purely for convenience and cleaner looking code.

The inferred init's properties/call would always be the same as if an initialiser wasn't written for the struct - i.e. not polymorphic, this can be done via extension.

This does have similarity to SE-0018, however, that proposal was still specifying parameters in the init which could lead to ordering issues etc. inferred could be clearer than memberwise.

The inferred init wouldn't necessarily allow changes to scope of the init without a subsequent proposal.

A major use case would be with SwiftUI Views, where function calls etc within the init, would be needed in a Struct as opposed to a Class.

Thoughts welcome :slight_smile: (or removal if this has been raised already).

3

This is tangential to Explicit Memberwise Initializers.