struct-env 🌱

𝒉𝒂𝒏𝒅𝒍𝒊𝒏𝒈 𝒆𝒏𝒗𝒊𝒓𝒐𝒏𝒎𝒆𝒏𝒕 𝒗𝒂𝒓𝒊𝒂𝒃𝒍𝒆𝒔 𝒊𝒏 𝒂 𝒕𝒚𝒑𝒆-𝒔𝒂𝒇𝒆 𝒘𝒂𝒚.

NOTE: Minimum Supported Zig Version is 0.12.0-dev.2058+04ac028a2

What is struct-env

struct-env provides a way to handle environment variables using struct fields. Its advantage is the automatic deserialization of environment variables into the specified types. For example, instead of using std.mem.eql(u8, foo, "true") to determine the truth value of an env-var, struct-env allows us to simply use foo: bool to deserialize it into a boolean type.

Quick Start

Below is a basic example:

const std = @import("std");
const struct_env = @import("struct-env");

const MyEnv = struct {
    home: []const u8,
    foo: ?[]const u8,
    bar: []const u8 = "bar",
};

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

    const env = try struct_env.fromEnv(allocator, MyEnv);
    defer struct_env.free(allocator, env);

    std.debug.print("HOME is {s}\n", .{env.home});
    std.debug.print("FOO  is {any}\n", .{env.foo == null});
    std.debug.print("BAR  is {s}\n", .{env.bar});
}

Here are some examples of this program's output. You can find more examples in the examples directory.

$ zig run [file]
HOME is /home/username
FOO  is true
BAR  is bar

$ FOO="foo" BAR="bar" zig run [file]
HOME is /home/username
FOO  is false
BAR  is bar

struct-env assumes that there is an environment variable corresponding to each struct field, with the same name in all uppercase letters. For instance, a struct field foo_bar would be expected to have an environment variable named FOO_BAR.

Structs with fields of type Optional(? prefix) can be successfully deserialized even if their associated environment variable is not present.

Of course, if the variable does not exist, you can set a default value.

struct-env also supports deserializing slice from comma separated env var values.

Env-var with common prefix

The common pattern for prefixeing env var names for a specific app is supported using the fromPrefixedEnv. Asumming your env vars are prefixed with APP_, the example may look like

const MyEnv = struct {
    // APP_NAME
    name : []const u8,
};

const env = try struct_env.fromPrefixedEnv(allocator, MyEnv, "APP_");
defer struct_env.free(allocator, env);

Supported types:

• Built-in types, such as []const u8, i32
• Optional types, such as ?u32
• Slice types, such as [][]const u8

Installation

Add struct-env as dependency in build.zig.zon:

.{
    .name = "my-project",
    .version = "0.1.0",
    .dependencies = .{
       .struct_env= .{
           .url = "https://github.com/Hanaasagi/struct-env/archive/refs/tags/v0.2.0.tar.gz",
           .hash = "1220224c50ca0178c6061fb96721fc331ed1136641ebb8a86cff55cc74481d66a4b9",
       },
    },
}

Expose struct-env as a module in build.zig:

diff --git a/build.zig b/build.zig
index 60fb4c2..0255ef3 100644
--- a/build.zig
+++ b/build.zig
@@ -15,6 +15,9 @@ pub fn build(b: *std.Build) void {
     // set a preferred release mode, allowing the user to decide how to optimize.
     const optimize = b.standardOptimizeOption(.{});

+    const opts = .{ .target = target, .optimize = optimize };
+    const struct_env_module = b.dependency("struct_env", opts).module("struct-env");
+
     const exe = b.addExecutable(.{
         .name = "m",
         // In this case the main source file is merely a path, however, in more
@@ -23,6 +26,7 @@ pub fn build(b: *std.Build) void {
         .target = target,
         .optimize = optimize,
     });
+    exe.addModule("struct-env", struct_env_module);

     // This declares intent for the executable to be installed into the
     // standard location when the user invokes the "install" step (the default

License

MIT

---

Thanks to those who have helped me on Reddit and Stack Overflow.