Error: access of union field 'Pointer' while field 'Optional' is active

Hello i’m new to zig.
I’m writing a simple toy program that echo back what user input.

const std = @import("std");
// const print = std.debug.print;

pub fn main() !void {
    const allocator = std.heap.page_allocator;

    const w =;
    const r =;
    while (true) {
        try w.print("> ", .{});
        const input = try r.readUntilDelimiterOrEofAlloc(allocator, '\n', 1024);
        if (input) |s| {
            try w.print("said: {s}\n", .{s});

but it doesn’t compile. it says.

/home/linuxbrew/.linuxbrew/Cellar/zig/HEAD-30eb2a1/lib/zig/std/mem/Allocator.zig:488:45: error: access of union field 'Pointer' while field 'Optional' is active
    const Slice = @typeInfo(@TypeOf(memory)).Pointer;
/home/linuxbrew/.linuxbrew/Cellar/zig/HEAD-30eb2a1/lib/zig/std/builtin.zig:193:18: note: union declared here
pub const Type = union(enum) {
referenced by:
    main: /home/q/Dev/zig/playground/src/main.zig:12:24
    callMain: /home/linuxbrew/.linuxbrew/Cellar/zig/HEAD-30eb2a1/lib/zig/std/start.zig:614:32
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

line 12 is where i’m freeing the input. so if i don’t free the input the program compiles. what did i do wrong?

input is an optional so you have to access its value via .? in the free call:


The error message most definitely does not help.

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