From 21ea23271a2e10f81cd993d4065d7a5a846e1099 Mon Sep 17 00:00:00 2001
From: Meghan Denny <hello@nektro.net>
Date: Wed, 5 Feb 2025 03:12:41 -0800
Subject: [PATCH] add lessThanBy

---
 src/lessThanBy.zig | 20 ++++++++++++++++++++
 src/lib.zig        |  1 +
 src/sortBy.zig     |  6 +-----
 3 files changed, 22 insertions(+), 5 deletions(-)
 create mode 100644 src/lessThanBy.zig

diff --git a/src/lessThanBy.zig b/src/lessThanBy.zig
new file mode 100644
index 0000000000000000000000000000000000000000..e88be4c28612796bf55a1c64b084a7ba9dd9f209
--- /dev/null
+++ b/src/lessThanBy.zig
@@ -0,0 +1,20 @@
+const std = @import("std");
+const string = []const u8;
+const extras = @import("./lib.zig");
+
+pub fn lessThanBy(comptime T: type, comptime field: std.meta.FieldEnum(T)) fn (void, T, T) bool {
+    const S = struct {
+        pub fn lessThan(_: void, lhs: T, rhs: T) bool {
+            return @field(lhs, @tagName(field)) < @field(rhs, @tagName(field));
+        }
+    };
+    return S.lessThan;
+}
+
+test {
+    const S = struct { x: u32 };
+    const l = lessThanBy(S, .x);
+    try std.testing.expect(l({}, .{ .x = 19 }, .{ .x = 53 }));
+    try std.testing.expect(!l({}, .{ .x = 44 }, .{ .x = 44 }));
+    try std.testing.expect(!l({}, .{ .x = 89 }, .{ .x = 26 }));
+}
diff --git a/src/lib.zig b/src/lib.zig
index 1ff181a17a3da960fe67986f399cb5f341ee4384..63bfa8efd344049127924efd0c29342726b3f669 100644
--- a/src/lib.zig
+++ b/src/lib.zig
@@ -101,3 +101,4 @@ pub usingnamespace @import("./isSlice.zig");
 pub usingnamespace @import("./matchesNone.zig");
 pub usingnamespace @import("./indexOfSlice.zig");
 pub usingnamespace @import("./mapBy.zig");
+pub usingnamespace @import("./lessThanBy.zig");
diff --git a/src/sortBy.zig b/src/sortBy.zig
index 91c8c91d6240521987d42a31ad590eb61570d96d..8b166a7b95dadf344a7235abdef67caeadc5b8cc 100644
--- a/src/sortBy.zig
+++ b/src/sortBy.zig
@@ -3,11 +3,7 @@ const string = []const u8;
 const extras = @import("./lib.zig");
 
 pub fn sortBy(comptime T: type, items: []T, comptime field: std.meta.FieldEnum(T)) void {
-    std.mem.sort(T, items, {}, struct {
-        fn f(_: void, lhs: T, rhs: T) bool {
-            return @field(lhs, @tagName(field)) < @field(rhs, @tagName(field));
-        }
-    }.f);
+    std.mem.sort(T, items, {}, extras.lessThanBy(T, field));
 }
 
 test {
-- 
2.54.0