pointer's capability • it extends the scope of pointee to Callable objects • it's not nullable $ ^{1} $ cannot be used as non-type template parameter yet Works in constexpr, just like function type • sizeof(T*) function_ref (as of P0792R5) • nullable • reference semantics • type-erased • at least 2x the size std::function • nullable • value semantics • type-erased • only larger

transform(convertIntToString); 7: } ## Add a guard to nullable in - fix one of the asserts X Add null checks ✗ )) 3: i = 9; 4: std::cout << "i=" << i << " prints 9\n"; • views::nullable — Extra safety for maybe-like types — std::optional, shared_ptr, raw ptrs, result of find (?) ## How does this work? 01: template nullable=""> 02: class nullable_view

63 Dynamic type ..... 64 Platform types ..... 64 2.1.8 Nullable types ..... 64 Nullability lozenge ..... 65 Definitely non-nullable types ..... 66 2.1.9 Intersection types ..... 67 2.1.10 intersection types ..... 70 2.3.4 Subtyping for integer literal types ..... 70 2.3.5 Subtyping for nullable types ..... 71 2.4 Upper and lower bounds ..... 73 2.4.1 Least upper bound ..... 73 2.4.2 (Kotlin MPP) feature. The type system of Kotlin distinguishes at compile time between nullable and non-nullable types, achieving null-safety, i.e., guaranteeing the absence of runtime errors caused by

Adding a non-nullable field to a populated table ..... 44 15.1.1. Adding a NOT NULL field ..... 44 15.1.2. Adding a CHECKed column ..... 46 15.1.3. Using domains to add a non-nullable field ..... columns non-nullable ..... 47 15.2.1. Making an existing column NOT NULL ..... 48 15.2.2. Adding a CHECK constraint to an existing column ..... 48 15.3. Making non-nullable columns nullable again .. '', etc ..... 60 Primary key with NULL entries ..... 61 SUBSTRING results described as non-nullable ..... 61 Gbak -n restoring NOT NULL ..... 61 IN, = ANY and = SOME with indexed subselect ..

// nullable var nullable_value: ?[] const u8 = null; assert(nullable_value == null); warn("\nnullable 1\ntype: {} ", @運名@typeOf(nullable_value)), nullable_value); nullable_value nullable_value = "hi"; assert(nullable_value != null); } warn("\nnullable 2\ntype: {} \n", @運Name(@typeOf(nullable_value)), nullable_value); // error union var number_or_error: error!i32 = error build-exe values.zig $ ./values 1 + 1 = 2 7.0 / 3.0 = 2.33333325 false true false nullable 1 type: ?[]const u8 value: null nullable 2 type: ?[]const u8 value: hi error union 1 type: error!i32 value: error.ArgNotFound

true); } // nullable const nullable_value = if (os.args.count() >= 2) os.args.at(1) else null; %%io.stdout.printf("\nnullable\ntype: {} \nvalue: {} ", @運名@(typeOf(nullable_value)), nullable_value); number_or_error); $ zig build-exe values.zig $ ./values 1 + 1 = 2 7.0 / 3.0 = 2.333333 false true false nullable type: ?[]const u8 value: null error union type: %[]const u8 value: error.ArgNotFound ## Primitive Primitive Values |Name|Description| |---|---| |true and false|bool values| |null|used to set a nullable type to null| |undefined|used to leave a value unspecified| |this|refers to the thing in immediate

Data classes ..... 85 Practice ..... 87 Next step ..... 88 Null safety ..... 88 Nullable types ..... 88 Check for null values ..... 89 Use safe calls ..... 89 Use Elvis operator while loop ..... 337 when expression ..... 338 Ranges ..... 338 Collections ..... 339 Nullable values and null checks ..... 339 Type checks and automatic casts ..... 340 Comments .... 344 Get first item of a possibly empty collection ..... 344 Execute if not null ..... 344 Map nullable value if not null ..... 344 Return on when statement ..... 344 try-catch expression ..... 345

default value instead of throwing an exception. val map = mapOf("key" to 42) // returns non-nullable Int value 42 val value: Int = map.getValue("key") val mapWithDefault = map.withDefault as an expression: fun maxOf(a: Int, b: Int) = if (a > b) a else b See if-expressions. Using nullable values and checking for null A reference must be explicitly marked as null when null value is possible does not hold an integer: fun parseInt(str: String): Int? { // ... } Use a function returning nullable value: fun printProduct(arg1: String, arg2: String) { val x = parseInt(arg1) val y = parseInt(arg2)

LE_NAME) VARCHAR(253) NullableMON$PAGE_SIZE(RDB$PAGE_SIZE) SMALLINT NullableMON$ODS_MAJOR(RDB$ODS_NUMBER) SMALLINT NullableMON$O R) SMALLINT NullableMON$OLDEST_TRANSACTION(RDB$TRANSACTION_ID) INTEGER NullableMON$OLDEST_ACTIVE(RDB$TRANSACTION_ID) INTEGER NullableNullableMON$NEXT_TRANSACTION(RDB$TRANSACTION_ID) INTEGER NullableMON$PAGE_BUFFERS(RDB$PAGE_BUFFERS) INTEGER Nullable<

default value instead of throwing an exception. val map = mapOf("key" to 42) // returns non-nullable Int value 42 val value: Int = map.getValue("key") val mapWithDefault = map.withDefault used as an expression: fun maxOf(a: Int, b: Int) = if (a > b) a else b See if-expressions. ## Nullable values and null checks A reference must be explicitly marked as null when null value is possible does not hold an integer: fun parseInt(str: String): Int? { // ... } Use a function returning nullable value: fun printProduct(arg1: String, arg2: String) { val x = parseInt(arg1) val y = parseInt(arg2)