PG.swift example of https://gist.github.com/brentdax/fe23d4d9b0fdf8cd1949094f6ef1a936

InterpolationExample.swift

// original:
Query("SELECT * FROM example WHERE e_uuid = $1;", idA)
// or
Query("SELECT * FROM example WHERE e_uuid = $1;", [idA])

// manual interpolation test:
var query = Query(stringInterpolation: {
	var temp = Query.StringInterpolation(totalLiteralSize: 40, interpolationCount: 1)
	temp.appendLiteral("SELECT * FROM example WHERE e_uuid = ")
	temp.appendInterpolation(idA)
	temp.appendLiteral(";")
	return temp
}())

// proposed compiler feature:
var query: Query = "SELECT * FROM example WHERE e_uuid = \(idA);"

PG+Interpolation.swift

// note Query already impliments ExpressibleByStringLiteral

public protocol ExpressibleByStringInterpolation: ExpressibleByStringLiteral {
	associatedtype StringInterpolation: StringInterpolationProtocol
	where StringInterpolation.StringLiteralType == StringLiteralType
	
	init(stringInterpolation: StringInterpolation)
}

public protocol StringInterpolationProtocol {
	associatedtype StringLiteralType : _ExpressibleByBuiltinStringLiteral
	
	init(totalLiteralSize literalCodeUnits: Int, interpolationCount: Int)
	
	mutating func appendLiteral(_ literal: StringLiteralType)
	
	mutating func appendInterpolation(_ binding: PostgresCodable?)
}


extension Query: ExpressibleByStringInterpolation {
	public typealias StringInterpolation = _StringInterpolation
	
	public struct _StringInterpolation: StringInterpolationProtocol {
		public typealias StringInterpolation = String
		
		var string: String = ""
		var bindings: [PostgresCodable?] = []
		
		public init(totalLiteralSize literalCodeUnits: Int, interpolationCount: Int) {
			self.string.reserveCapacity(literalCodeUnits)
			self.bindings.reserveCapacity(interpolationCount)
		}
		
		public mutating func appendLiteral(_ literal: String) {
			string.append(literal)
		}
		
		public mutating func appendInterpolation(_ binding: PostgresCodable?) {
			bindings.append(binding)
			// intentionally starting with $1
			string.append("$\(bindings.count)")
		}
	}
	
	public init(stringInterpolation: StringInterpolation) {
		self.init(stringInterpolation.string, bindings: stringInterpolation.bindings)
	}
}