70 lines
2.1 KiB
Zig
70 lines
2.1 KiB
Zig
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//
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// Understanding how Zig treats numeric literals is fundamental
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// and important, but it isn't exactly exciting.
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//
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// We're about to get into the cool wizard stuff that makes
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// programming computers fun. But first, let's introduce a new and
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// vital Zig keyword:
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//
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// comptime
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//
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// When you put 'comptime' in front of a variable declaration,
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// function parameter, or expression, you're saying, "I want Zig
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// to evaluate this at compile time rather than runtime."
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//
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// We've already seen that Zig implicitly performs certain types
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// of evaluations at compile time. (Many compilers do a certain
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// amount of this, but Zig is explicit about it.) Therefore,
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// these two statements are equivalent and using the 'comptime'
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// keyword here is redundant:
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//
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// const foo1 = 5;
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// comptime const foo2 = 5;
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//
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// But here it makes a difference:
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//
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// var bar1 = 5; // ERROR!
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// comptime var bar2 = 5; // OKAY!
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//
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// 'bar1' gives us an error because Zig assumes mutable
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// identifiers will be used at runtime and trying to use a
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// comptime_int of undetermined size at runtime is basically a
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// MEMORY CRIME and you are UNDER ARREST.
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//
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// 'bar2' is okay because we've told Zig that this identifier
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// MUST be resolvable at compile time. Now Zig won't yell at us
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// for assigning a comptime_int to it without a specific runtime
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// size.
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//
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// The comptime property is also INFECTIOUS. Once you declare
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// something to be comptime, Zig will always either:
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//
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// 1. Be able to resolve that thing at compile time.
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// 2. Yell at you.
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//
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const print = @import("std").debug.print;
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pub fn main() void {
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//
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// In this contrived example, we've decided to allocate some
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// arrays using a variable count!
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//
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// Please make this work. Please?
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//
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var count = 0;
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count += 1;
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var a1: [count]u8 = .{'A'} ** count;
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count += 1;
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var a2: [count]u8 = .{'B'} ** count;
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count += 1;
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var a3: [count]u8 = .{'C'} ** count;
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count += 1;
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var a4: [count]u8 = .{'D'} ** count;
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print("{s} {s} {s} {s}\n", .{a1, a2, a3, a4});
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}
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