function pointers must be single pointers

Question

Trying to build a simple router, where a given function is called based on the required route, so for testing I started with the below:

// routes.zig
const std = @import("std");

//pub const LoadFunction = fn (i32) f32;
pub fn init(routeRegister: *std.StringHashMap(fn (i32) f32)) !void {
    try routeRegister.put("/load", load);
}

pub fn load(i: i32) f32 {
    std.log.info("file is loaded, {}", .{i});
    return 0.1;
}

And in the main function I have:

        var routeRegister = std.StringHashMap(fn (i32) f32).init(allocator);
        try routes.init(&routeRegister);
        defer routeRegister.deinit();

        if (routeRegister.get(target)) |handler| {
            std.debug.print("Calling handler: {s} for route: {s}\n", .{ handler, target });
///** Here I want to call the function `load` if the target route is `/load` **///
        } else {
            log.err("Unknown route: {s}", .{target});
            return error.ErrorNoEntity;
        }

• First of all I got the below error while compiling:

[hasany@hasan-20tes1n300 src]$ zig run main.zig
/usr/lib/zig/std/hash_map.zig:539:41: error: parameter of type 'fn(i32) f32' must be declared comptime
        pub fn put(self: *Self, key: K, value: V) Allocator.Error!void {
                                        ^~~~~~~~
/usr/lib/zig/std/hash_map.zig:539:41: note: use '*const fn(i32) f32' for a function pointer type
referenced by:
    init: routes.zig:5:22
    handleRequest: main.zig:117:19
    remaining reference traces hidden; use '-freference-trace' to see all reference traces
/usr/lib/zig/std/hash_map.zig:752:24: error: function pointers must be single pointers
            values: [*]V,
                       ^

• Second, how can I envoke the function load "which is defined at the hashmap, once I get the matched key, which is in my case /load?

Answer 1

You use a function body instead of a function pointer. The compiler even tells you:

hash_map.zig:539:41: note: use '*const fn(i32) f32' for a function pointer type

Second, how can I envoke the function load "which is defined at the hashmap, once I get the matched key, which is in my case /load?

Simply call it as any other function:

handler(i);