Change the way of determining the MRO algorithm used from an enum

defined in the header, to a pointer to a structure. This allows the
flexibility to easily add more MROs in the future, and to provide an
API to do so. Dispatch in mro.c is now via the structure pointed to,
rather than switch statements on the value of the enum.

p4raw-id: //depot/perl@31977

1 files changed, 39 insertions, 25 deletions

diff --git a/mro.c b/mro.c
index 4f850f4ea3..525076f2eb 100644
--- a/mro.c
+++ b/mro.c
@@ -24,6 +24,31 @@ These functions are related to the method resolution order of perl classes
 #define PERL_IN_MRO_C
 #include "perl.h"
 
+struct mro_alg {
+    const char *name;
+    AV *(*resolve)(pTHX_ HV* stash, I32 level);
+};
+
+/* First one is the default */
+static struct mro_alg mros[] = {
+    {"dfs", S_mro_get_linear_isa_dfs},
+    {"c3", S_mro_get_linear_isa_c3}
+};
+
+#define NUMBER_OF_MROS (sizeof(mros)/sizeof(struct mro_alg))
+
+static const struct mro_alg *
+S_get_mro_from_name(pTHX_ const char *const name) {
+    const struct mro_alg *algo = mros;
+    const struct mro_alg *const end = mros + NUMBER_OF_MROS;
+    while (algo < end) {
+	if(strEQ(name, algo->name))
+	    return algo;
+	++algo;
+    }
+    return NULL;
+}
+
 struct mro_meta*
 Perl_mro_meta_init(pTHX_ HV* stash)
 {
@@ -36,6 +61,7 @@ Perl_mro_meta_init(pTHX_ HV* stash)
     HvAUX(stash)->xhv_mro_meta = newmeta;
     newmeta->cache_gen = 1;
     newmeta->pkg_gen = 1;
+    newmeta->mro_which = (void *) mros;
 
     return newmeta;
 }
@@ -427,14 +453,9 @@ Perl_mro_get_linear_isa(pTHX_ HV *stash)
         Perl_croak(aTHX_ "Can't linearize anonymous symbol table");
 
     meta = HvMROMETA(stash);
-    if(meta->mro_which == MRO_DFS) {
-        return mro_get_linear_isa_dfs(stash, 0);
-    } else if(meta->mro_which == MRO_C3) {
-        return mro_get_linear_isa_c3(stash, 0);
-    } else {
+    if (!meta->mro_which)
         Perl_croak(aTHX_ "panic: invalid MRO!");
-    }
-    return NULL; /* NOT REACHED */
+    return meta->mro_which->resolve(aTHX_ stash, 0);
 }
 
 /*
@@ -694,12 +715,10 @@ XS(XS_mro_get_linear_isa) {
     }
     else if(items > 1) {
         const char* const which = SvPV_nolen(ST(1));
-        if(strEQ(which, "dfs"))
-            RETVAL = mro_get_linear_isa_dfs(class_stash, 0);
-        else if(strEQ(which, "c3"))
-            RETVAL = mro_get_linear_isa_c3(class_stash, 0);
-        else
-            Perl_croak(aTHX_ "Invalid mro name: '%s'", which);
+	const struct mro_alg *const algo = S_get_mro_from_name(aTHX_ which);
+	if (!algo)
+	    Perl_croak(aTHX_ "Invalid mro name: '%s'", which);
+	algo->resolve(aTHX_ class_stash, 0);
     }
     else {
         RETVAL = mro_get_linear_isa(class_stash);
@@ -715,8 +734,8 @@ XS(XS_mro_set_mro)
     dVAR;
     dXSARGS;
     SV* classname;
-    char* whichstr;
-    mro_alg which;
+    const char* whichstr;
+    const struct mro_alg *which;
     HV* class_stash;
     struct mro_meta* meta;
 
@@ -731,11 +750,8 @@ XS(XS_mro_set_mro)
     if(!class_stash) Perl_croak(aTHX_ "Cannot create class: '%"SVf"'!", SVfARG(classname));
     meta = HvMROMETA(class_stash);
 
-    if(strEQ(whichstr, "dfs"))
-        which = MRO_DFS;
-    else if(strEQ(whichstr, "c3"))
-        which = MRO_C3;
-    else
+    which = S_get_mro_from_name(aTHX_ whichstr);
+    if (!which)
         Perl_croak(aTHX_ "Invalid mro name: '%s'", whichstr);
 
     if(meta->mro_which != which) {
@@ -766,11 +782,9 @@ XS(XS_mro_get_mro)
     classname = ST(0);
     class_stash = gv_stashsv(classname, 0);
 
-    if(!class_stash || HvMROMETA(class_stash)->mro_which == MRO_DFS)
-        ST(0) = sv_2mortal(newSVpvn("dfs", 3));
-    else
-        ST(0) = sv_2mortal(newSVpvn("c3", 2));
-
+    ST(0) = sv_2mortal(newSVpv(class_stash
+			       ? HvMROMETA(class_stash)->mro_which->name
+			       : "dfs", 0));
     XSRETURN(1);
 }