From: Nobuyoshi Nakada <nobu@...>
Date: 2008-10-14T20:31:12+09:00
Subject: [ruby-core:19328] Re: [Feature #643] __DIR__

Hi,

At Tue, 14 Oct 2008 04:20:18 +0900,
Nikolai Weibull wrote in [ruby-core:19319]:
> I realize that I'm responding to a joke, but wouldn't it perhaps be
> nice if File.dirname took an optional second argument that allowed you
> to specify how many levels up you want to go?

I like this idea too.

> I actually implemented this at work, simply because I was doing a lot
> of nested File.dirname calls.

This is my patch.


Index: file.c
===================================================================
--- file.c	(revision 19773)
+++ file.c	(working copy)
@@ -2523,4 +2523,32 @@ rb_path_last_separator(const char *path)
 
 static char *
+path_last_nth_separator(const char *pstart, const char *pend, int nth)
+{
+    enum {lastmax = 16};
+    char *lastbuf[lastmax];
+
+    if (nth <= 0) return (char *)pend;
+    do {
+	int lastidx = 0;
+	const char *path = pstart;
+	while (path < pend && *path) {
+	    if (isdirsep(*path)) {
+		const char *tmp = path++;
+		while (isdirsep(*path)) path++;
+		if (!*path) break;
+		lastbuf[lastidx++ % lastmax] = (char *)tmp;
+	    }
+	    else {
+		path = CharNext(path);
+	    }
+	}
+	if (lastidx < nth) return NULL;
+	if (nth <= lastmax) return lastbuf[(lastidx - nth) % lastmax];
+	pend = lastbuf[lastidx % lastmax];
+    } while ((nth -= lastmax) > 0);
+    return (char *)pend;
+}
+
+static char *
 chompdirsep(const char *path)
 {
@@ -3060,4 +3088,6 @@ rb_file_s_basename(int argc, VALUE *argv
 }
 
+static VALUE rb_file_dirname(VALUE fname, int nth);
+
 /*
  *  call-seq:
@@ -3073,11 +3103,22 @@ rb_file_s_basename(int argc, VALUE *argv
 
 static VALUE
-rb_file_s_dirname(VALUE klass, VALUE fname)
+rb_file_s_dirname(int argc, VALUE *argv, VALUE klass)
+{
+    VALUE fname, level;
+    int nth;
+
+    rb_scan_args(argc, argv, "11", &fname, &level);
+    nth = NUM2INT(level);
+    FilePathStringValue(fname);
+    return rb_file_dirname(fname, nth);
+}
+
+static VALUE
+rb_file_dirname(VALUE fname, int nth)
 {
     const char *name, *root, *p;
     VALUE dirname;
 
-    FilePathStringValue(fname);
-    name = StringValueCStr(fname);
+    name = RSTRING_PTR(fname);
     root = skiproot(name);
 #ifdef DOSISH_UNC
@@ -3088,5 +3129,21 @@ rb_file_s_dirname(VALUE klass, VALUE fna
 	name = root - 1;
 #endif
-    p = strrdirsep(root);
+    if (nth < 0) {
+	const char *tmp = p = root;
+	while (++nth < 0) {
+	    while (isdirsep(*tmp)) tmp++;
+	    if (!(tmp = nextdirsep(p = tmp))) break;
+	    p = tmp;
+	}
+    }
+    else if (nth == 0) {
+	p = chompdirsep(root);
+    }
+    else if (nth == 1) {
+	p = strrdirsep(root);
+    }
+    else {
+	p = path_last_nth_separator(root, name + RSTRING_LEN(fname), nth);
+    }
     if (!p) {
 	p = root;
@@ -3209,5 +3266,5 @@ rb_file_s_split(VALUE klass, VALUE path)
 {
     FilePathStringValue(path);		/* get rid of converting twice */
-    return rb_assoc_new(rb_file_s_dirname(Qnil, path), rb_file_s_basename(1,&path));
+    return rb_assoc_new(rb_file_dirname(path, 1), rb_file_s_basename(1,&path));
 }
 
@@ -4709,5 +4766,5 @@ Init_File(void)
     rb_define_singleton_method(rb_cFile, "absolute_path", rb_file_s_absolute_path, -1);
     rb_define_singleton_method(rb_cFile, "basename", rb_file_s_basename, -1);
-    rb_define_singleton_method(rb_cFile, "dirname", rb_file_s_dirname, 1);
+    rb_define_singleton_method(rb_cFile, "dirname", rb_file_s_dirname, -1);
     rb_define_singleton_method(rb_cFile, "extname", rb_file_s_extname, 1);
     rb_define_singleton_method(rb_cFile, "path", rb_file_s_path, 1);


-- 
Nobu Nakada