Swift: Global constant naming convention?

I've been debating using camel case with a leading capital for class-level constants. For example:

static let MaximumNumberOfLoginAttempts = 10

It's still camel-case (as Apple appears to recommend), but the capitalized leading character makes it clear that the value is immutable.

Apple advocates the camelCase. That said, many use _camelCase just to differentiate it especially if you are likely to have the same name at a lower scope.

Swift 3 API guidelines state that "Names of types and protocols are UpperCamelCase. Everything else is lowerCamelCase."

https://swift.org/documentation/api-design-guidelines/

Ideally your global constants will be located within an enum, extension, or struct of some sort, which would be UpperCamelCase, and all properties in that space would be lowerCamelCase.

struct LoginConstants {
    static let maxAttempts = 10
}

And accessed like so,

if attempts > LoginConstants.maxAttempts { ...}

(credit to Ryan Maloney's answer for calling out the benefits of enum)

To improve on bmjohns answer, it's better to use an enum instead of a struct to act as a namespace for your constants. An enum with no cases can't be instantiated, whereas a struct can. If it is a struct, then instantiating it (via LoginConstants()) is allowed, but that has no meaning and doesn't make sense to do.

The convention is to use enumerations for namespacing, as such:

enum LoginConstants {
    static let maxAttempts = 10
}

This ensures that the only valid usage of LoginConstants is for accessing its static members.