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63 lines
2.0 KiB
Zig
63 lines
2.0 KiB
Zig
//
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// In addition to knowing when to use the 'comptime' keyword,
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// it's also good to know when you DON'T need it.
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//
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// The following contexts are already IMPLICITLY evaluated at
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// compile time, and adding the 'comptime' keyword would be
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// superfluous, redundant, and smelly:
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//
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// * The container-level scope (outside of any function in a source file)
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// * Type declarations of:
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// * Variables
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// * Functions (types of parameters and return values)
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// * Structs
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// * Unions
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// * Enums
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// * The test expressions in inline for and while loops
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// * An expression passed to the @cImport() builtin
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//
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// Work with Zig for a while, and you'll start to develop an
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// intuition for these contexts. Let's work on that now.
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//
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// You have been given just one 'comptime' statement to use in
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// the program below. Here it is:
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//
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// comptime
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//
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// Just one is all it takes. Use it wisely!
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//
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const print = @import("std").debug.print;
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// Being in the container-level scope, everything about this value is
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// implicitly required to be known compile time.
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const llama_count = 5;
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// Again, this value's type and size must be known at compile
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// time, but we're letting the compiler infer both from the
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// return type of a function.
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const llamas = makeLlamas(llama_count);
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// And here's the function. Note that the return value type
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// depends on one of the input arguments!
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fn makeLlamas(count: usize) [count]u8 {
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var temp: [count]u8 = undefined;
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var i = 0;
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// Note that this does NOT need to be an inline 'while'.
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while (i < count) : (i += 1) {
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temp[i] = i;
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}
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return temp;
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}
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pub fn main() void {
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print("My llama value is {}.\n", .{llamas[2]});
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}
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//
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// The lesson here is to not pepper your program with 'comptime'
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// keywords unless you need them. Between the implicit compile
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// time contexts and Zig's aggressive evaluation of any
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// expression it can figure out at compile time, it's sometimes
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// surprising how few places actually need the keyword.
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