explicit_init - creating an instance from a meta-type

[evgeniyd]

Creating an instance from meta-types via explicit init() is a common idiom. Currently, swiftlint highlights instructions like this when explicit_init rule is opted-in.

struct SomeStruct {
    var a: Int = 0
}

class SomeClass {
    var a: Int = 0
    
    required init() {
        a = 1
    }
}

let metaType = SomeClass.self // SomeClass.Type
let instance = metaType.init()

let structMetaType =  SomeStruct.self // SomeStruct.Type
let structInstance = structMetaType.init()

[marcelofabri]

Are you sure this example triggers? I couldn't reproduce on SwiftLint 0.13.2:

$ swiftlint lint --path file.swift          
Loading configuration from '.swiftlint.yml'
Linting Swift files at path file.swift
Linting 'file.swift' (1/1)
file.swift:2:2: error: Variable Name Violation: Variable name should be between 3 and 40 characters long: 'a' (variable_name)
file.swift:6:2: error: Variable Name Violation: Variable name should be between 3 and 40 characters long: 'a' (variable_name)
Done linting! Found 2 violations, 2 serious in 1 file.

[evgeniyd]

@marcelofabri my fault, I didn't do linting, just shown the idiom.

Here is the snipped that does produce the warning:

import UIKit.UIView

public enum KeyImage {
    case standard
    case customView(type: UIView.Type)
}

extension KeyImage {
    public func view() -> UIView {
        switch self {
        case .standard:
            return StandardView()
        case .customView(let ViewType):
            return ViewType.init()
        }
    }
}

class StandardView: UIView { }
class MyView: UIView { }

KeyImage.standard.view()
KeyImage.customView(type: MyView.self).view()

Output:

$ swiftlint lint --path file.swift
Loading configuration from '.swiftlint.yml'
Linting Swift files at path file.swift
Linting 'file.swift' (1/1)
file.swift:14:28: warning: Explicit Init Violation: Explicitly calling .init() should be avoided. (explicit_init)
Done linting! Found 1 violation, 0 serious in 1 file.

[marcelofabri]

The rule currently uses a regex to check if it's a type or metatype, so changing ViewType to viewType fixes the issue.

It would be better to check if it was indeed a type or variable, but we currently don't have this information AFAIK and both a type (UIView) and a variable (viewType) have the same SyntaxKind: source.lang.swift.syntaxtype.identifier.

[evgeniyd]

@marcelofabri Thank you for explanation. I thought it is possible to infer the type, as swiftlint hooked into Clang and SourceKit.

Unfortunately, lowercasing the var name here loses the semantics I'd like to preserve. Nevertheless, this particular example, could be fixed in this way, I have other cases, where I was in need to go with // swiftlint:disable:this explicit_init.

[jpsim]

I thought it is possible to infer the type, as swiftlint hooked into Clang and SourceKit.

Possible yes, but not implemented. Would require a new "compiled" mode that SwiftLint could run in such as the one described in #829 (comment).

[stale]

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