Re: PATCH: 3.1.5 - sample associative array implementation

["Bart Schaefer" <schaefer@brasslantern.com>]

Thanks for looking at this, Peter.

On Nov 11,  2:58pm, Peter Stephenson wrote:
} Subject: Re: PATCH: 3.1.5 - sample associative array implementation
}
} "Bart Schaefer" wrote:
} > However, there are some caveats:  (1) You can't assign to multiple elements
} > of an associative array in a single expression; you must always use the
} > subscript syntax.
} 
} One question is whether
}   hash=(key1 val1 key2 val2)
} replaces the array entirely, or just adds/replaces those elements.

The problem with that syntax is that you can't tell whether `hash' is
intended to be an associative array, so you still have to declare it
first.  (Perl handles this by always prefixing variable names with $
@ or % even when assigning.)

The more lispy
    hash=((key1 val1) (key2 val2))
appears to be syntactically invalid at present ("number expected" ??).
However, it appears that it WAS valid in 3.0.5, so perhaps that's a bug
in 3.1.5.

} In
} the former case it's difficult to think of a way of replacing multiple
} elements at once [...]
} Another thing:  there's no way of getting the keys of the hash.

What's needed is a syntax to have the hash produce its key/value pairs
in the appropriate form so that you can do e.g.

    hash=(${(kv)hash} key1 newval1 key2 newval2)

(where ${(k)hash} means substitute the keys, and ${(v)hash} the values,
which is also the default when (k) is not present).

Then simply decree that, after the whole hash is replaced, elements are
assigned in left-to-right order, replacing duplicates.  Then you can do

    hash=(key 1 newval1 key2 newval2 ${(kv)hash})

to insert key1 and key2 only if they were not already present.

} Something like $hash[(k)*] would be OK, except that * and @ don't seem
} to work with flags at the moment.

I think an expansion flag rather than a subscription flag is the way,
see sample above.

} > I'm afraid there may be some memory leaks in the code to form
} > arrays from the values.
} 
} I put in a MUSTUSEHEAP to check for this.  It hasn't printed a message
} so far.

What I'm worried about is that copyparam() uses PERMALLOC, but I think
the pointers that it returns are being placed in a heap-allocated array
in some cases.  There's also a ztrdup() in scancopyparams().  MUSTUSEHEAP
wouldn't report either problem.  This would come up e.g. when you have a
local with the same name as an existing hash, so you have to save and
restore the hash.

} > When an associative array element is referenced, it's hash table slot is
} > created and initially marked PM_UNSET.
} 
} This means (post patch):
} 
} % typeset -H hash
} % hash[one]=eins
} % print $hash[two]
} 
} % print -l "$hash[@]"
} one
}                        <- $hash[two] was created unset
} % 
} 
} Is this really correct?

We can fix that by changing the way the hashtable scan happens, so it
ignores unset parameters.  The patch below fixes this, and adds some
support for the ${(k)hash} substitution flag, but I didn't actually put
in those flags themselves.

Will v->pm->flags &= ~PM_UNSET hurt anything in setstrvalue()?  It didn't
seem as if it should, but there are many details I don't understand.

} > (5) $assoc[bread,3] produces "but" (the first 3 characters of the
} > value) which I think is because getarg() doesn't return soon enough; it
} > really ought to either ignore or gripe about what comes after the comma.
} 
} I haven't touched this.

I no longer think it's as simple as I previously thought, so I didn't do
any more with it either.

This patch of course requires both my previous one and Peter's.

Index: Src/params.c
===================================================================
--- params.c	1998/11/11 17:40:25	1.5
+++ params.c	1998/11/11 18:14:34
@@ -295,13 +295,21 @@
     return nht;
 }
 
+#define SCANPM_WANTVALS   (1<<0)
+#define SCANPM_WANTKEYS   (1<<1)
+#define SCANPM_WANTINDEX  (1<<2)
+
 static unsigned numparamvals;
 
 /**/
 static void
 scancountparams(HashNode hn, int flags)
 {
-    ++numparamvals;
+    if (!(((Param)hn)->flags & PM_UNSET)) {
+	++numparamvals;
+	if ((flags & SCANPM_WANTKEYS) && (flags & SCANPM_WANTVALS))
+	    ++numparamvals;
+    }
 }
 
 static char **paramvals;
@@ -311,26 +319,33 @@
 scanparamvals(HashNode hn, int flags)
 {
     struct value v;
-    v.isarr = (flags & 1);
     v.pm = (Param)hn;
-    v.inv = (flags & 2);
-    v.a = 0;
-    v.b = -1;
-    paramvals[numparamvals++] = getstrvalue(&v);
+    if (!(v.pm->flags & PM_UNSET)) {
+	if (flags & SCANPM_WANTKEYS) {
+	    paramvals[numparamvals++] = v.pm->nam;
+	    if (!(flags & SCANPM_WANTVALS))
+		return;
+	}
+	v.isarr = (PM_TYPE(v.pm->flags) & (PM_ARRAY|PM_HASHED));
+	v.inv = (flags & SCANPM_WANTINDEX);
+	v.a = 0;
+	v.b = -1;
+	paramvals[numparamvals++] = getstrvalue(&v);
+    }
 }
 
 /**/
 char **
-paramvalarr(HashTable ht)
+paramvalarr(HashTable ht, unsigned flags)
 {
     MUSTUSEHEAP("paramvalarr");
     numparamvals = 0;
     if (ht)
-	scanhashtable(ht, 0, 0, 0, scancountparams, 0);
+	scanhashtable(ht, 0, 0, 0, scancountparams, flags);
     paramvals = (char **) alloc(numparamvals * sizeof(char **) + 1);
     if (ht) {
 	numparamvals = 0;
-	scanhashtable(ht, 0, 0, 0, scanparamvals, 0);
+	scanhashtable(ht, 0, 0, 0, scanparamvals, flags);
     }
     paramvals[numparamvals] = 0;
     return paramvals;
@@ -348,7 +363,7 @@
     else if (PM_TYPE(v->pm->flags) == PM_ARRAY)
 	return v->arr = v->pm->gets.afn(v->pm);
     else if (PM_TYPE(v->pm->flags) == PM_HASHED)
-	return v->arr = paramvalarr(v->pm->gets.hfn(v->pm));
+	return v->arr = paramvalarr(v->pm->gets.hfn(v->pm), 0);
     else
 	return NULL;
 }
@@ -1133,6 +1148,7 @@
 	zsfree(val);
 	return;
     }
+    v->pm->flags &= ~PM_UNSET;
     switch (PM_TYPE(v->pm->flags)) {
     case PM_SCALAR:
 	MUSTUSEHEAP("setstrvalue");

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com