thefail.ooc

g: func <T> (T: Class) -> String { "" }

f: func {
    match(t := g(String)) {
        case a: String => a println()
        case => "n" println()
    }
}

thefailingcode.c

void m5__f() {
    
    {
        lang_String__String* t = m5__g((lang_types__Class*) (lang_String__String_class()));
        lang_String__String* __matchcompare2 = (t); // wrong scope!
    }
    if (lang_types__Object_instanceOf__quest((lang_types__Object*) (t), (lang_types__Class*) (lang_String__String_class()))){
        lang_String__String* a = NULL;
        a = ((lang_String__String*) ((t)));
        lang_String__String_println(a);
    } else {
        lang_String__String_println(__strLit215);
    };
}

thepatch.diff

diff --git a/source/rock/middle/Match.ooc b/source/rock/middle/Match.ooc
index 14a69f0..87cf3cf 100644
--- a/source/rock/middle/Match.ooc
+++ b/source/rock/middle/Match.ooc
@@ -10,6 +10,7 @@ Match: class extends Expression {
 
     type: Type = null
     expr: Expression = null
+    compareExpr: Expression = null
     cases := ArrayList<Case> new()
 
     casesResolved := 0
@@ -78,6 +79,16 @@ Match: class extends Expression {
             casesSize = cases getSize()
         }
 
+        if(compareExpr == null && expr != null) {
+            // set a "compare expression".
+            compareDecl := VariableDecl new(type, generateTempName("matchcompare"), expr, token)
+            compareExpr = VariableAccess new(compareDecl, token)
+            if(!trail addBeforeInScope(this, compareDecl)) {
+                res throwError(CouldntAddBeforeInScope new(token, this, compareDecl, trail))
+            }
+            // success! we can now use `compareExpr` later on.
+        }
+
         catchAll? := false
 
         if(casesResolved < casesSize) {
@@ -144,7 +155,9 @@ Match: class extends Expression {
                                 if (caze getExpr() instanceOf?(BinaryOp)) {
                                     unwrapBinaryOpCase(caze)
                                 } else {
-                                    caze setExpr(Comparison new(expr, caze getExpr(), CompType equal, caseToken))
+                                    // use the "compare" expression here to avoid multiple
+                                    // function calls.
+                                    caze setExpr(Comparison new(compareExpr, caze getExpr(), CompType equal, caseToken))
                                 }
                             }
                         }