7 files changed, 87 insertions, 74 deletions

diff --git a/README.md b/README.md
index 3156539..ad9f026 100644
--- a/README.md
+++ b/README.md
@@ -25,8 +25,8 @@ into master on every `zig` release.
 The simplest way to use this library is to just call the `clap.parse` function.
 
 ```zig
-const std = @import("std");
 const clap = @import("clap");
+const std = @import("std");
 
 const debug = std.debug;
 
@@ -41,11 +41,10 @@ pub fn main() !void {
     };
 
     // Initalize our diagnostics, which can be used for reporting useful errors.
-    // This is optional. You can also just pass `null` to `parser.next` if you
-    // don't care about the extra information `Diagnostics` provides.
-    var diag: clap.Diagnostic = undefined;
-
-    var args = clap.parse(clap.Help, &params, std.heap.page_allocator, &diag) catch |err| {
+    // This is optional. You can also pass `.{}` to `clap.parse` if you don't
+    // care about the extra information `Diagnostics` provides.
+    var diag = clap.Diagnostic{};
+    var args = clap.parse(clap.Help, &params, .{ .diagnostic = &diag }) catch |err| {
         // Report useful error and exit
         diag.report(std.io.getStdErr().outStream(), err) catch {};
         return err;
@@ -107,8 +106,8 @@ The `StreamingClap` is the base of all the other parsers. It's a streaming parse
 `args.Iterator` to provide it with arguments lazily.
 
 ```zig
-const std = @import("std");
 const clap = @import("clap");
+const std = @import("std");
 
 const debug = std.debug;
 
@@ -137,19 +136,18 @@ pub fn main() !void {
     var iter = try clap.args.OsIterator.init(allocator);
     defer iter.deinit();
 
-    // Initialize our streaming parser.
+    // Initalize our diagnostics, which can be used for reporting useful errors.
+    // This is optional. You can also leave the `diagnostic` field unset if you
+    // don't care about the extra information `Diagnostic` provides.
+    var diag = clap.Diagnostic{};
     var parser = clap.StreamingClap(u8, clap.args.OsIterator){
         .params = &params,
         .iter = &iter,
+        .diagnostic = &diag,
     };
 
-    // Initalize our diagnostics, which can be used for reporting useful errors.
-    // This is optional. You can also just pass `null` to `parser.next` if you
-    // don't care about the extra information `Diagnostics` provides.
-    var diag: clap.Diagnostic = undefined;
-
     // Because we use a streaming parser, we have to consume each argument parsed individually.
-    while (parser.next(&diag) catch |err| {
+    while (parser.next() catch |err| {
         // Report useful error and exit
         diag.report(std.io.getStdErr().outStream(), err) catch {};
         return err;
diff --git a/clap.zig b/clap.zig
index 4548a48..b31cd1d 100644
--- a/clap.zig
+++ b/clap.zig
@@ -1,6 +1,7 @@
 const std = @import("std");
 
 const debug = std.debug;
+const heap = std.heap;
 const io = std.io;
 const mem = std.mem;
 const testing = std.testing;
@@ -307,7 +308,6 @@ pub fn Args(comptime Id: type, comptime params: []const Param(Id)) type {
         exe_arg: ?[]const u8,
 
         pub fn deinit(a: *@This()) void {
-            a.clap.deinit();
             a.arena.deinit();
         }
 
@@ -329,20 +329,37 @@ pub fn Args(comptime Id: type, comptime params: []const Param(Id)) type {
     };
 }
 
+/// Options that can be set to customize the behavior of parsing.
+pub const ParseOptions = struct {
+    /// The allocator used for all memory allocations. Defaults to the `heap.page_allocator`.
+    /// Note: You should probably override this allocator if you are calling `parseEx`. Unlike
+    ///       `parse`, `parseEx` does not wrap the allocator so the heap allocator can be
+    ///       quite expensive. (TODO: Can we pick a better default? For `parse`, this allocator
+    ///       is fine, as it wraps it in an arena)
+    allocator: *mem.Allocator = heap.page_allocator,
+    diagnostic: ?*Diagnostic = null,
+};
+
 /// Same as `parseEx` but uses the `args.OsIterator` by default.
 pub fn parse(
     comptime Id: type,
     comptime params: []const Param(Id),
-    allocator: *mem.Allocator,
-    diag: ?*Diagnostic,
+    opt: ParseOptions,
 ) !Args(Id, params) {
-    var iter = try args.OsIterator.init(allocator);
-    const clap = try parseEx(Id, params, allocator, &iter, diag);
-    return Args(Id, params){
+    var iter = try args.OsIterator.init(opt.allocator);
+    var res = Args(Id, params){
         .arena = iter.arena,
-        .clap = clap,
         .exe_arg = iter.exe_arg,
+        .clap = undefined,
     };
+
+    // Let's reuse the arena from the `OSIterator` since we already have
+    // it.
+    res.clap = try parseEx(Id, params, &iter, .{
+        .allocator = &res.arena.allocator,
+        .diagnostic = opt.diagnostic,
+    });
+    return res;
 }
 
 /// Parses the command line arguments passed into the program based on an
@@ -350,12 +367,11 @@ pub fn parse(
 pub fn parseEx(
     comptime Id: type,
     comptime params: []const Param(Id),
-    allocator: *mem.Allocator,
     iter: anytype,
-    diag: ?*Diagnostic,
+    opt: ParseOptions,
 ) !ComptimeClap(Id, params) {
     const Clap = ComptimeClap(Id, params);
-    return try Clap.parse(allocator, iter, diag);
+    return try Clap.parse(iter, opt);
 }
 
 /// Will print a help message in the following format:
diff --git a/clap/comptime.zig b/clap/comptime.zig
index 8ab61cb..9bec38e 100644
--- a/clap/comptime.zig
+++ b/clap/comptime.zig
@@ -1,10 +1,10 @@
 const clap = @import("../clap.zig");
 const std = @import("std");
 
-const testing = std.testing;
+const debug = std.debug;
 const heap = std.heap;
 const mem = std.mem;
-const debug = std.debug;
+const testing = std.testing;
 
 /// Deprecated: Use `parseEx` instead
 pub fn ComptimeClap(
@@ -42,7 +42,8 @@ pub fn ComptimeClap(
         pos: []const []const u8,
         allocator: *mem.Allocator,
 
-        pub fn parse(allocator: *mem.Allocator, iter: anytype, diag: ?*clap.Diagnostic) !@This() {
+        pub fn parse(iter: anytype, opt: clap.ParseOptions) !@This() {
+            const allocator = opt.allocator;
             var multis = [_]std.ArrayList([]const u8){undefined} ** multi_options;
             for (multis) |*multi| {
                 multi.* = std.ArrayList([]const u8).init(allocator);
@@ -62,7 +63,7 @@ pub fn ComptimeClap(
                 .params = converted_params,
                 .iter = iter,
             };
-            while (try stream.next(diag)) |arg| {
+            while (try stream.next()) |arg| {
                 const param = arg.param;
                 if (param.names.long == null and param.names.short == null) {
                     try pos.append(arg.value.?);
@@ -81,19 +82,17 @@ pub fn ComptimeClap(
                 }
             }
 
-            for (multis) |*multi, i| {
+            for (multis) |*multi, i|
                 res.multi_options[i] = multi.toOwnedSlice();
-            }
             res.pos = pos.toOwnedSlice();
 
             return res;
         }
 
-        pub fn deinit(parser: *@This()) void {
+        pub fn deinit(parser: @This()) void {
             for (parser.multi_options) |o|
                 parser.allocator.free(o);
             parser.allocator.free(parser.pos);
-            parser.* = undefined;
         }
 
         pub fn flag(parser: @This(), comptime name: []const u8) bool {
@@ -155,14 +154,12 @@ test "" {
         clap.parseParam("<P>") catch unreachable,
     });
 
-    var buf: [1024]u8 = undefined;
-    var fb_allocator = heap.FixedBufferAllocator.init(buf[0..]);
     var iter = clap.args.SliceIterator{
         .args = &[_][]const u8{
             "-a", "-c", "0", "something", "-d", "a", "--dd", "b",
         },
     };
-    var args = try Clap.parse(&fb_allocator.allocator, &iter, null);
+    var args = try Clap.parse(&iter, .{ .allocator = testing.allocator });
     defer args.deinit();
 
     testing.expect(args.flag("-a"));
diff --git a/clap/streaming.zig b/clap/streaming.zig
index 11145f0..8030a67 100644
--- a/clap/streaming.zig
+++ b/clap/streaming.zig
@@ -40,12 +40,13 @@ pub fn StreamingClap(comptime Id: type, comptime ArgIterator: type) type {
         iter: *ArgIterator,
         state: State = .normal,
         positional: ?*const clap.Param(Id) = null,
+        diagnostic: ?*clap.Diagnostic = null,
 
         /// Get the next Arg that matches a Param.
-        pub fn next(parser: *@This(), diag: ?*clap.Diagnostic) !?Arg(Id) {
+        pub fn next(parser: *@This()) !?Arg(Id) {
             switch (parser.state) {
-                .normal => return try parser.normal(diag),
-                .chaining => |state| return try parser.chainging(state, diag),
+                .normal => return try parser.normal(),
+                .chaining => |state| return try parser.chainging(state),
                 .rest_are_positional => {
                     const param = parser.positionalParam() orelse unreachable;
                     const value = (try parser.iter.next()) orelse return null;
@@ -54,7 +55,7 @@ pub fn StreamingClap(comptime Id: type, comptime ArgIterator: type) type {
             }
         }
 
-        fn normal(parser: *@This(), diag: ?*clap.Diagnostic) !?Arg(Id) {
+        fn normal(parser: *@This()) !?Arg(Id) {
             const arg_info = (try parser.parseNextArg()) orelse return null;
             const arg = arg_info.arg;
             switch (arg_info.kind) {
@@ -70,7 +71,7 @@ pub fn StreamingClap(comptime Id: type, comptime ArgIterator: type) type {
                             continue;
                         if (param.takes_value == .None) {
                             if (maybe_value != null)
-                                return err(diag, arg, .{ .long = name }, error.DoesntTakeValue);
+                                return parser.err(arg, .{ .long = name }, error.DoesntTakeValue);
 
                             return Arg(Id){ .param = param };
                         }
@@ -80,18 +81,18 @@ pub fn StreamingClap(comptime Id: type, comptime ArgIterator: type) type {
                                 break :blk v;
 
                             break :blk (try parser.iter.next()) orelse
-                                return err(diag, arg, .{ .long = name }, error.MissingValue);
+                                return parser.err(arg, .{ .long = name }, error.MissingValue);
                         };
 
                         return Arg(Id){ .param = param, .value = value };
                     }
 
-                    return err(diag, arg, .{ .long = name }, error.InvalidArgument);
+                    return parser.err(arg, .{ .long = name }, error.InvalidArgument);
                 },
                 .short => return try parser.chainging(.{
                     .arg = arg,
                     .index = 0,
-                }, diag),
+                }),
                 .positional => if (parser.positionalParam()) |param| {
                     // If we find a positional with the value `--` then we
                     // interpret the rest of the arguments as positional
@@ -104,12 +105,12 @@ pub fn StreamingClap(comptime Id: type, comptime ArgIterator: type) type {
 
                     return Arg(Id){ .param = param, .value = arg };
                 } else {
-                    return err(diag, arg, .{}, error.InvalidArgument);
+                    return parser.err(arg, .{}, error.InvalidArgument);
                 },
             }
         }
 
-        fn chainging(parser: *@This(), state: State.Chaining, diag: ?*clap.Diagnostic) !?Arg(Id) {
+        fn chainging(parser: *@This(), state: State.Chaining) !?Arg(Id) {
             const arg = state.arg;
             const index = state.index;
             const next_index = index + 1;
@@ -136,13 +137,13 @@ pub fn StreamingClap(comptime Id: type, comptime ArgIterator: type) type {
                 const next_is_eql = if (next_index < arg.len) arg[next_index] == '=' else false;
                 if (param.takes_value == .None) {
                     if (next_is_eql)
-                        return err(diag, arg, .{ .short = short }, error.DoesntTakeValue);
+                        return parser.err(arg, .{ .short = short }, error.DoesntTakeValue);
                     return Arg(Id){ .param = param };
                 }
 
                 if (arg.len <= next_index) {
                     const value = (try parser.iter.next()) orelse
-                        return err(diag, arg, .{ .short = short }, error.MissingValue);
+                        return parser.err(arg, .{ .short = short }, error.MissingValue);
 
                     return Arg(Id){ .param = param, .value = value };
                 }
@@ -153,7 +154,7 @@ pub fn StreamingClap(comptime Id: type, comptime ArgIterator: type) type {
                 return Arg(Id){ .param = param, .value = arg[next_index..] };
             }
 
-            return err(diag, arg, .{ .short = arg[index] }, error.InvalidArgument);
+            return parser.err(arg, .{ .short = arg[index] }, error.InvalidArgument);
         }
 
         fn positionalParam(parser: *@This()) ?*const clap.Param(Id) {
@@ -194,8 +195,8 @@ pub fn StreamingClap(comptime Id: type, comptime ArgIterator: type) type {
             return ArgInfo{ .arg = full_arg, .kind = .positional };
         }
 
-        fn err(diag: ?*clap.Diagnostic, arg: []const u8, names: clap.Names, _err: anytype) @TypeOf(_err) {
-            if (diag) |d|
+        fn err(parser: @This(), arg: []const u8, names: clap.Names, _err: anytype) @TypeOf(_err) {
+            if (parser.diagnostic) |d|
                 d.* = .{ .arg = arg, .name = names };
             return _err;
         }
@@ -210,7 +211,7 @@ fn testNoErr(params: []const clap.Param(u8), args_strings: []const []const u8, r
     };
 
     for (results) |res| {
-        const arg = (c.next(null) catch unreachable) orelse unreachable;
+        const arg = (c.next() catch unreachable) orelse unreachable;
         testing.expectEqual(res.param, arg.param);
         const expected_value = res.value orelse {
             testing.expectEqual(@as(@TypeOf(arg.value), null), arg.value);
@@ -220,18 +221,19 @@ fn testNoErr(params: []const clap.Param(u8), args_strings: []const []const u8, r
         testing.expectEqualSlices(u8, expected_value, actual_value);
     }
 
-    if (c.next(null) catch unreachable) |_|
+    if (c.next() catch unreachable) |_|
         unreachable;
 }
 
 fn testErr(params: []const clap.Param(u8), args_strings: []const []const u8, expected: []const u8) void {
-    var diag: clap.Diagnostic = undefined;
+    var diag = clap.Diagnostic{};
     var iter = args.SliceIterator{ .args = args_strings };
     var c = StreamingClap(u8, args.SliceIterator){
         .params = params,
         .iter = &iter,
+        .diagnostic = &diag,
     };
-    while (c.next(&diag) catch |err| {
+    while (c.next() catch |err| {
         var buf: [1024]u8 = undefined;
         var slice_stream = io.fixedBufferStream(&buf);
         diag.report(slice_stream.outStream(), err) catch unreachable;
diff --git a/example/simple-ex.zig b/example/simple-ex.zig
index d6ecc44..f504d63 100644
--- a/example/simple-ex.zig
+++ b/example/simple-ex.zig
@@ -1,5 +1,5 @@
-const std = @import("std");
 const clap = @import("clap");
+const std = @import("std");
 
 const debug = std.debug;
 
@@ -21,11 +21,13 @@ pub fn main() !void {
     defer iter.deinit();
 
     // Initalize our diagnostics, which can be used for reporting useful errors.
-    // This is optional. You can also just pass `null` to `parser.next` if you
-    // don't care about the extra information `Diagnostics` provides.
-    var diag: clap.Diagnostic = undefined;
-
-    var args = clap.parseEx(clap.Help, &params, allocator, &iter, &diag) catch |err| {
+    // This is optional. You can also pass `.{}` to `clap.parse` if you don't
+    // care about the extra information `Diagnostics` provides.
+    var diag = clap.Diagnostic{};
+    var args = clap.parseEx(clap.Help, &params, &iter, .{
+        .allocator = allocator,
+        .diagnostic = &diag,
+    }) catch |err| {
         // Report useful error and exit
         diag.report(std.io.getStdErr().outStream(), err) catch {};
         return err;
diff --git a/example/simple.zig b/example/simple.zig
index 270e344..392dca3 100644
--- a/example/simple.zig
+++ b/example/simple.zig
@@ -1,5 +1,5 @@
-const std = @import("std");
 const clap = @import("clap");
+const std = @import("std");
 
 const debug = std.debug;
 
@@ -14,11 +14,10 @@ pub fn main() !void {
     };
 
     // Initalize our diagnostics, which can be used for reporting useful errors.
-    // This is optional. You can also just pass `null` to `parser.next` if you
-    // don't care about the extra information `Diagnostics` provides.
-    var diag: clap.Diagnostic = undefined;
-
-    var args = clap.parse(clap.Help, &params, std.heap.page_allocator, &diag) catch |err| {
+    // This is optional. You can also pass `.{}` to `clap.parse` if you don't
+    // care about the extra information `Diagnostics` provides.
+    var diag = clap.Diagnostic{};
+    var args = clap.parse(clap.Help, &params, .{ .diagnostic = &diag }) catch |err| {
         // Report useful error and exit
         diag.report(std.io.getStdErr().outStream(), err) catch {};
         return err;
diff --git a/example/streaming-clap.zig b/example/streaming-clap.zig
index 941070f..f8d873d 100644
--- a/example/streaming-clap.zig
+++ b/example/streaming-clap.zig
@@ -1,5 +1,5 @@
-const std = @import("std");
 const clap = @import("clap");
+const std = @import("std");
 
 const debug = std.debug;
 
@@ -28,19 +28,18 @@ pub fn main() !void {
     var iter = try clap.args.OsIterator.init(allocator);
     defer iter.deinit();
 
-    // Initialize our streaming parser.
+    // Initalize our diagnostics, which can be used for reporting useful errors.
+    // This is optional. You can also leave the `diagnostic` field unset if you
+    // don't care about the extra information `Diagnostic` provides.
+    var diag = clap.Diagnostic{};
     var parser = clap.StreamingClap(u8, clap.args.OsIterator){
         .params = &params,
         .iter = &iter,
+        .diagnostic = &diag,
     };
 
-    // Initalize our diagnostics, which can be used for reporting useful errors.
-    // This is optional. You can also just pass `null` to `parser.next` if you
-    // don't care about the extra information `Diagnostics` provides.
-    var diag: clap.Diagnostic = undefined;
-
     // Because we use a streaming parser, we have to consume each argument parsed individually.
-    while (parser.next(&diag) catch |err| {
+    while (parser.next() catch |err| {
         // Report useful error and exit
         diag.report(std.io.getStdErr().outStream(), err) catch {};
         return err;