Type casting (typecast)

Keyword typecast is used for explicit casting type A to type B (value typecast T)

Example

120 typecast i8 // i64 (int) -> i8

// Casting pointers
var x i64 = 120;
&x typecast *i8 // *i64 -> *i
?> // Resolves to i8

// Warning: useless typecast
120 typecast i64 // i64 -> i64

// Error: cannot cast type `int` to type `T1`
struct T1 ... end
120 typecast T1  // i64 -> T1

Cast types

Kind	Description
REINTERPRET	Does not modify the value — only its interpretation
TRUNCATE	Loses information — target is smaller than source
EXTEND	Adds information — target is larger than source
NORMALIZE_BOOL	Compares against zero — non-zero becomes true

Cast rules

From	To	Kind	Notes
*T	*U	REINTERPRET	Any pointer to any pointer
integer	*T	REINTERPRET	Integer size must equal pointer size (e.g. i64 on 64-bit)
*T	integer	REINTERPRET	Same constraint as above
bool	integer	REINTERPRET	Boolean invariant, extends to integer
T	T	REINTERPRET	Both integer or char, same byte size (e.g. i8 → char)
T	T	TRUNCATE	Both integer or char, source bigger than target (e.g. i64 → i8)
T	T	EXTEND	Both integer or char, target bigger than source (e.g. i8 → i64)
integer	bool	NORMALIZE_BOOL	Non-zero → true, zero → false

Casts not listed above are rejected at compile time.

REINTERPRET

Does not modifies value, just another interpretation of bytes

• T -> T (any pointer to any pointer)
• integer -> *T (treating integer as pointer requires integer size to be same as target architecture pointer size, such on 64bit, integer must be i64, as others has invariant pointer)
• *T -> integer (same as int -> *T)
• bool -> integer (therefore, booleans invariants integer, it does extends to integer)
• T -> T, where both are integer nor char and their byte size is same (i8 -> char)

TRUNCATE

Cast with losing information

• T -> T, where both are integer nor char and source type byte size is bigger (i64 -> i8)

EXTEND

Cast without losing information: add additonal bytes

• T -> T, where both are integer nor char and target type byte size is bigger (i8 -> i64)

NORMALIZE_BOOL

Does compares value against zero, true on non-zero value

• integer -> bool