Fix a few Swift 4.1 warnings.

Author: MrMage

Sources/SQLite/Typed/Coding.swift

@@ -217,7 +217,7 @@ fileprivate class SQLiteDecoder : Decoder {
         }
 
         var allKeys: [Key] {
-            return self.row.columnNames.keys.flatMap({Key(stringValue: $0)})
+            return self.row.columnNames.keys.compactMap({Key(stringValue: $0)})
         }
 
         func contains(_ key: Key) -> Bool {

Sources/SQLite/Typed/CoreFunctions.swift

@@ -637,7 +637,7 @@ extension ExpressionType where UnderlyingType == String? {
 
 }
 
-extension Collection where Iterator.Element : Value, IndexDistance == Int {
+extension Collection where Iterator.Element : Value {
 
     /// Builds a copy of the expression prepended with an `IN` check against the
     /// collection.

Sources/SQLite/Typed/Query.swift

@@ -647,7 +647,7 @@ extension QueryType {
             whereClause
         ]
 
-        return Insert(" ".join(clauses.flatMap { $0 }).expression)
+        return Insert(" ".join(clauses.compactMap { $0 }).expression)
     }
 
     /// Runs an `INSERT` statement against the query with `DEFAULT VALUES`.
@@ -690,7 +690,7 @@ extension QueryType {
             limitOffsetClause
         ]
 
-        return Update(" ".join(clauses.flatMap { $0 }).expression)
+        return Update(" ".join(clauses.compactMap { $0 }).expression)
     }
 
     // MARK: DELETE
@@ -704,7 +704,7 @@ extension QueryType {
             limitOffsetClause
         ]
 
-        return Delete(" ".join(clauses.flatMap { $0 }).expression)
+        return Delete(" ".join(clauses.compactMap { $0 }).expression)
     }
 
     // MARK: EXISTS
@@ -789,7 +789,7 @@ extension QueryType {
             limitOffsetClause
         ]
 
-        return " ".join(clauses.flatMap { $0 }).expression
+        return " ".join(clauses.compactMap { $0 }).expression
     }
 
 }

Sources/SQLite/Typed/Schema.swift

@@ -47,7 +47,7 @@ extension Table {
             withoutRowid ? Expression<Void>(literal: "WITHOUT ROWID") : nil
         ]
 
-        return " ".join(clauses.flatMap { $0 }).asSQL()
+        return " ".join(clauses.compactMap { $0 }).asSQL()
     }
 
     public func create(_ query: QueryType, temporary: Bool = false, ifNotExists: Bool = false) -> String {
@@ -57,7 +57,7 @@ extension Table {
             query
         ]
 
-        return " ".join(clauses.flatMap { $0 }).asSQL()
+        return " ".join(clauses.compactMap { $0 }).asSQL()
     }
 
     // MARK: - ALTER TABLE … ADD COLUMN
@@ -135,7 +135,7 @@ extension Table {
             "".wrap(columns) as Expression<Void>
         ]
 
-        return " ".join(clauses.flatMap { $0 }).asSQL()
+        return " ".join(clauses.compactMap { $0 }).asSQL()
     }
 
     // MARK: - DROP INDEX
@@ -174,7 +174,7 @@ extension View {
             query
         ]
 
-        return " ".join(clauses.flatMap { $0 }).asSQL()
+        return " ".join(clauses.compactMap { $0 }).asSQL()
     }
 
     // MARK: - DROP VIEW
@@ -196,7 +196,7 @@ extension VirtualTable {
             using
         ]
 
-        return " ".join(clauses.flatMap { $0 }).asSQL()
+        return " ".join(clauses.compactMap { $0 }).asSQL()
     }
 
     // MARK: - ALTER TABLE … RENAME TO
@@ -405,7 +405,7 @@ public final class TableBuilder {
             delete.map { Expression<Void>(literal: "ON DELETE \($0.rawValue)") }
         ]
 
-        definitions.append(" ".join(clauses.flatMap { $0 }))
+        definitions.append(" ".join(clauses.compactMap { $0 }))
     }
 
 }
@@ -456,7 +456,7 @@ private extension QueryType {
             name
         ]
 
-        return " ".join(clauses.flatMap { $0 })
+        return " ".join(clauses.compactMap { $0 })
     }
 
     func rename(to: Self) -> String {
@@ -475,7 +475,7 @@ private extension QueryType {
             name
         ]
 
-        return " ".join(clauses.flatMap { $0 }).asSQL()
+        return " ".join(clauses.compactMap { $0 }).asSQL()
     }
 
 }
@@ -493,7 +493,7 @@ private func definition(_ column: Expressible, _ datatype: String, _ primaryKey:
         collate.map { " ".join([Expression<Void>(literal: "COLLATE"), $0]) }
     ]
 
-    return " ".join(clauses.flatMap { $0 })
+    return " ".join(clauses.compactMap { $0 })
 }
 
 private func reference(_ primary: (QueryType, Expressible)) -> Expressible {