Added error logic to the cast as String conversion.

Added more detailed error handling in the casting of string values to type of T. 

If decoding fails, instead of providing a generic message. Provides the user with clearer type error messages. 

More explicit failure state for casting from string to bool. 
If the user does not provide exactly values which are valid. Alert them to this issue.

Author: FoxClock

Sources/SQLClientSwift/SQLRowDecoder.swift

@@ -149,8 +149,13 @@ private struct SQLRowKeyedContainer<Key: CodingKey>: KeyedDecodingContainerProto
     }
 
     private func cast<T>(_ key: Key) throws -> T {
+        // Validate key is in columns
         let value = try requireValue(for: key)
+
+        // Direct cast as type 
         if let v = value as? T { return v }
+        
+        // If type is NSNumber supported
         if let n = value as? NSNumber {
             switch T.self {
             case is Bool.Type:   return (n.boolValue)   as! T
@@ -169,14 +174,40 @@ private struct SQLRowKeyedContainer<Key: CodingKey>: KeyedDecodingContainerProto
             default: break
             }
         }
+       // String → primitive conversions.
         if let s = value as? String {
             switch T.self {
-            case is Int.Type:    if let i = Int(s)    { return i as! T }
-            case is Double.Type: if let d = Double(s) { return d as! T }
-            case is Bool.Type:   return (["true","1","yes"].contains(s.lowercased())) as! T
+            case is Int.Type:
+                guard let i = Int(s) else {
+                    throw DecodingError.typeMismatch(T.self, .init(
+                        codingPath: codingPath + [key],
+                        debugDescription: "Cannot convert '\(s)' to Int for column '\(key.stringValue)'."))
+                }
+                return i as! T
+
+            case is Double.Type:
+                guard let d = Double(s) else {
+                    throw DecodingError.typeMismatch(T.self, .init(
+                        codingPath: codingPath + [key],
+                        debugDescription: "Cannot convert '\(s)' to Double for column '\(key.stringValue)'."))
+                }
+                return d as! T
+
+            case is Bool.Type:
+                switch s.lowercased() {
+                case "true",  "1", "yes": return true  as! T
+                case "false", "0", "no":  return false as! T
+                default:
+                    throw DecodingError.typeMismatch(T.self, .init(
+                        codingPath: codingPath + [key],
+                        debugDescription: "Cannot convert '\(s)' to Bool for column '\(key.stringValue)'. "
+                            + "Expected one of: true, false, 1, 0, yes, no."))
+                }
+
             default: break
             }
         }
+        // No Conversion path succeeded
         throw DecodingError.typeMismatch(T.self, .init(
             codingPath: codingPath + [key],
             debugDescription: "Expected \(T.self), got \(type(of: value)) for column '\(key.stringValue)'"))