Run time

Program start and end

A program runs in these steps:

1. The global variables are initialized, in the order of the files and of their declarations (see declarations).
2. Main runs, with the command-line arguments (without the program’s name) if it takes string[] args.
3. The program ends when Main returns, when Environment.Exit(code) is called or with a panic.

End	Exit code
void Main() returns	0
an integer Main returns n	n
Error<int> Main() returns a value n	n
Error<int> Main() returns a failure	1, after writing error: <message> to stderr
Environment.Exit(code)	code
a panic	101

When Main returns, the global variables are released and buffered output is written. Environment.Exit and a panic end the program right away: nothing is released and no Dispose runs, but buffered output is still written. Threads that are still running when the program ends are stopped.

Panics

A panic ends the program because of a bug. It writes panic: <reason> and the place to stderr and exits with code 101:

panic: array index out of range (index 5, length 3)
  at src/Game/World.cshift:482:21 in World.GetTile

The place is the file (as the compiler was given it; in a project, relative to the project folder), line, column and function. When a function of the standard library panics because of its arguments, the line called from ... shows where the program called it. A panic cannot be caught; errors that a program is expected to handle are Error<T> results.

These checks panic:

Reason	When
integer overflow	an integer operation or conversion whose result does not fit, in checked code (see below)
division by zero	an integer / or % by 0 (also in unchecked code)
array index out of range, string index out of range, slice index out of range, fixed array index out of range	an index outside of 0 .. Length - 1 (also in unchecked code); the message shows the index and the length
slice range out of bounds	a range a[i..j] that is not inside of the array or string
negative array length	new T[n] with n < 0
call of a null function	calling an Action/Func that is null
SharedPtr.Get(): the pointer is null	Get() or Ptr() of a null SharedPtr
the union 'U' holds no value	calling an interface method on a union that holds no value (its default value; is and switch simply match no member)
the collection for 'Fixed<T, N>' does not have N elements	converting a collection of another length to a Fixed
out of memory	an allocation failed
cannot create a thread	start could not create an OS thread
the message of Environment.Panic(message)	always

null strings and arrays are empty, not errors: their Length is 0, and indexing them panics with an index out of range. Reading a pointer, a stack overflow or an infinite recursion is not checked.

Checked and unchecked arithmetic

By default, integer arithmetic (+ - *, unary -, the compound assignments) and integer conversions with a cast are checked: a result that does not fit in the type panics with integer overflow. In unchecked code they wrap around (modulo 2^n), like in C. Unchecked code is:

• an unchecked { } block or an unchecked(e) expression;
• a whole program compiled with --unchecked, or a project with "unchecked": true in cshift.json (--checked turns it back on for one build). This applies to the program’s own files; the standard library stays checked.

Division by zero and index checks are made in unchecked code too. Shifts never panic: the count is masked (see expressions). Floating-point arithmetic follows IEEE 754 and never panics (1.0 / 0 is infinity, 0.0 / 0 NaN).

Targets

The compiler generates native code for:

Target	Pointer size (nint)	Notes
Linux x64	8	via LLVM / clang
Windows x64	8	via LLVM / clang, MinGW-w64
AmigaOS, --target m68k-amigaos	4	CShift’s own 68000 backend; AmigaOS libraries from NDK SFD files
WebAssembly, --target wasm32-wasi	4	via LLVM / clang with wasi-libc; no threads, no other programs (WebAssembly)

The sizes of the other types (int is always int32, long always int64, …) do not depend on the target, and integers are stored in the target’s byte order (little-endian on x64, big-endian on the 68000). The Amiga namespace of the standard library exists only for AmigaOS. The compiler options and the toolchain are described in the README.