Add [dict getdef] alias

doc/dict.n

@@ -120,6 +120,22 @@ It is an error to attempt to retrieve a value for a key that is not
 present in the dictionary.
 .RE
 .TP
+\fBdict getdef \fIdictionaryValue \fR?\fIkey ...\fR? \fIkey default\fR
+.TP
+\fBdict getwithdefault \fIdictionaryValue \fR?\fIkey ...\fR? \fIkey default\fR
+.VS "8.7, TIP342"
+This behaves the same as \fBdict get\fR (with at least one \fIkey\fR
+argument), returning the value that the key path maps to in the
+dictionary \fIdictionaryValue\fR, except that instead of producing an
+error because the \fIkey\fR (or one of the \fIkey\fRs on the key path)
+is absent, it returns the \fIdefault\fR argument instead.
+.RS
+.PP
+Note that there must always be at least one \fIkey\fR provided, and that
+\fBdict getdef\fR and \fBdict getwithdefault\fR are aliases for each other.
+.RE
+.VE "8.7, TIP342"
+.TP
 \fBdict incr \fIdictionaryVariable key \fR?\fIincrement\fR?
 .
 This adds the given increment value (an integer that defaults to 1 if

generic/tclDictObj.c

@@ -34,6 +34,8 @@ static int		DictFilterCmd(ClientData dummy, Tcl_Interp *interp,
 			    int objc, Tcl_Obj *const *objv);
 static int		DictGetCmd(ClientData dummy, Tcl_Interp *interp,
 			    int objc, Tcl_Obj *const *objv);
+static int		DictGetDefCmd(ClientData dummy, Tcl_Interp *interp,
+			    int objc, Tcl_Obj *const *objv);
 static int		DictIncrCmd(ClientData dummy, Tcl_Interp *interp,
 			    int objc, Tcl_Obj *const *objv);
 static int		DictInfoCmd(ClientData dummy, Tcl_Interp *interp,
@@ -89,6 +91,8 @@ static const EnsembleImplMap implementationMap[] = {
     {"filter",	DictFilterCmd,	NULL, NULL, NULL, 0 },
     {"for",	NULL,		TclCompileDictForCmd, DictForNRCmd, NULL, 0 },
     {"get",	DictGetCmd,	TclCompileDictGetCmd, NULL, NULL, 0 },
+    {"getdef",	DictGetDefCmd,	NULL, NULL, NULL, 0 },
+    {"getwithdefault",	DictGetDefCmd,	NULL, NULL, NULL, 0 },
     {"incr",	DictIncrCmd,	TclCompileDictIncrCmd, NULL, NULL, 0 },
     {"info",	DictInfoCmd,	TclCompileBasic1ArgCmd, NULL, NULL, 0 },
     {"keys",	DictKeysCmd,	TclCompileBasic1Or2ArgCmd, NULL, NULL, 0 },
@@ -1624,6 +1628,71 @@ DictGetCmd(
     return TCL_OK;
 }
 
+/*
+ *----------------------------------------------------------------------
+ *
+ * DictGetDefCmd --
+ *
+ *	This function implements the "dict getdef" and "dict getwithdefault"
+ *	Tcl commands. See the user documentation for details on what it does,
+ *	and TIP#342 for the formal specification.
+ *
+ * Results:
+ *	A standard Tcl result.
+ *
+ * Side effects:
+ *	See the user documentation.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+DictGetDefCmd(
+    ClientData dummy,
+    Tcl_Interp *interp,
+    int objc,
+    Tcl_Obj *const *objv)
+{
+    Tcl_Obj *dictPtr, *keyPtr, *valuePtr, *defaultPtr;
+    Tcl_Obj *const *keyPath;
+    int numKeys;
+
+    if (objc < 4) {
+	Tcl_WrongNumArgs(interp, 1, objv, "dictionary ?key ...? key default");
+	return TCL_ERROR;
+    }
+
+    /*
+     * Give the bits of arguments names for clarity.
+     */
+
+    dictPtr = objv[1];
+    keyPath = &objv[2];
+    numKeys = objc - 4;		/* Number of keys in keyPath; there's always
+				 * one extra key afterwards too. */
+    keyPtr = objv[objc - 2];
+    defaultPtr = objv[objc - 1];
+
+    /*
+     * Implement the getting-with-default operation.
+     */
+
+    dictPtr = TclTraceDictPath(interp, dictPtr, numKeys, keyPath,
+	    DICT_PATH_EXISTS);
+    if (dictPtr == NULL) {
+	return TCL_ERROR;
+    } else if (dictPtr == DICT_PATH_NON_EXISTENT) {
+	Tcl_SetObjResult(interp, defaultPtr);
+    } else if (Tcl_DictObjGet(interp, dictPtr, keyPtr, &valuePtr) != TCL_OK) {
+	return TCL_ERROR;
+    } else if (valuePtr == NULL) {
+	Tcl_SetObjResult(interp, defaultPtr);
+    } else {
+	Tcl_SetObjResult(interp, valuePtr);
+    }
+    return TCL_OK;
+}
+
 /*
  *----------------------------------------------------------------------
  *

tests/dict.test

@@ -2047,6 +2047,62 @@ test dict-25.1 {compiled dict update with low-refcount values [Bug d553228d9f]}
 	dict update item item item two two {}
     }}
 } {}
+
+test dict-26.1 {dict getdef command} -body {
+    dict getdef {a b} a c
+} -result b
+test dict-26.2 {dict getdef command} -body {
+    dict getdef {a b} b c
+} -result c
+test dict-26.3 {dict getdef command} -body {
+    dict getdef {a {b c}} a b d
+} -result c
+test dict-26.4 {dict getdef command} -body {
+    dict getdef {a {b c}} a c d
+} -result d
+test dict-26.5 {dict getdef command} -body {
+    dict getdef {a {b c}} b c d
+} -result d
+test dict-26.6 {dict getdef command} -returnCodes error -body {
+    dict getdef {a {b c d}} a b d
+} -result {missing value to go with key}
+test dict-26.7 {dict getdef command} -returnCodes error -body {
+    dict getdef
+} -result {wrong # args: should be "dict getdef dictionary ?key ...? key default"}
+test dict-26.8 {dict getdef command} -returnCodes error -body {
+    dict getdef {}
+} -result {wrong # args: should be "dict getdef dictionary ?key ...? key default"}
+test dict-26.9 {dict getdef command} -returnCodes error -body {
+    dict getdef {} {}
+} -result {wrong # args: should be "dict getdef dictionary ?key ...? key default"}
+
+test dict-27.1 {dict getwithdefault command} -body {
+    dict getwithdefault {a b} a c
+} -result b
+test dict-27.2 {dict getwithdefault command} -body {
+    dict getwithdefault {a b} b c
+} -result c
+test dict-27.3 {dict getwithdefault command} -body {
+    dict getwithdefault {a {b c}} a b d
+} -result c
+test dict-27.4 {dict getwithdefault command} -body {
+    dict getwithdefault {a {b c}} a c d
+} -result d
+test dict-27.5 {dict getwithdefault command} -body {
+    dict getwithdefault {a {b c}} b c d
+} -result d
+test dict-27.6 {dict getwithdefault command} -returnCodes error -body {
+    dict getwithdefault {a {b c d}} a b d
+} -result {missing value to go with key}
+test dict-27.7 {dict getwithdefault command} -returnCodes error -body {
+    dict getwithdefault
+} -result {wrong # args: should be "dict getwithdefault dictionary ?key ...? key default"}
+test dict-27.8 {dict getwithdefault command} -returnCodes error -body {
+    dict getwithdefault {}
+} -result {wrong # args: should be "dict getwithdefault dictionary ?key ...? key default"}
+test dict-27.9 {dict getwithdefault command} -returnCodes error -body {
+    dict getwithdefault {} {}
+} -result {wrong # args: should be "dict getwithdefault dictionary ?key ...? key default"}
 
 # cleanup
 ::tcltest::cleanupTests