const std       = @import("std");
var allocator   = std.heap.page_allocator;

const N = 1000;  // number of [M]T
const M = 10000; // length of each vector.

pub fn main() !void {

    var vec_of_vecs = std.ArrayList([]u32).init(allocator);
    defer vec_of_vecs.deinit();
    try vec_of_vecs.ensureCapacity(@intCast(u32, N+3)) ;

    var j: u32 = 0;
    while (j<N) : (j+=1) {

        var inner_buf = try allocator.alloc(u32, M);

        // This line is more or less the entire runtime length of the program.
        // But getting rid of the cast or writing a while loop doesn't change
        // anything. Does this code fail to vectorize when zig cc succeeds or
        // something?
        for (inner_buf) |_, index| inner_buf[index] = @intCast(u32, index);

        vec_of_vecs.appendAssumeCapacity(inner_buf);
    }

    for (vec_of_vecs.items) |inner_buf| {
        allocator.free(inner_buf);
    }
}