symbols.md

Symbols

Inject values instead of services.

Insprired by Apache Tapestry Symbols.

Concept

The general idea is that you define can define values that are injected by a SymbolKey into properties with the @Symbol annotation. This allows to separate the values from their usage. For example, we use it to have all API-related code in a shared dependency, but the correct host is defined as a symbol.

Like Registry, you provide a factory for the symbol creation.

Types of Symbols

There are three methods available:

• Symbols.constant: The symbol is a constant. Instead of a factory, the value can be provided directly.
• Symbols.lazy: The symbol is evaluated on first use.
• Symbols.dynamic: The symbol factory is evaluated on every access.

All three have the argument isDefault: Bool = false which marks the Symbol as overridable. Non-default Symbols can't be overriden and will throw a fatalError. Also, registering two default Symbols under the same key is forbidden.

SymbolKeys

Strings can be used to identify a Symbol. But to easier access all available Symbols, you should use a SymbolKey instead, by extending it:

import IntegralSwift

public extension SymbolKey {
    static let apiHost = SymbolKey("api-host")
}

@Symbol(.apiHost)
var host: String