Sunday, March 27, 2005

"Feature Creeps" in BMCS

This "Good Friday" weekend had been a "Good Hacking" weekend for me. I made good progress on the conversions between the primitive types.

As I was hacking, the following question constantly surfaced at the back of my head - "How will I be managing the features sneakily creeping in from gmcs world to the bmcs world?". There are two components to answering this question - Identifying that a feature is creeping in and tactfully "handling" the same.

To cite an example, "unsigned numeric types" are "feature creeps" from the C# world. The following pattern keeps recurring in the gmcs conversion routines.

static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
                               Type target_type, Location loc)
    Type expr_type = expr.Type;
    if (expr_type == TypeManager.ushort_type){
        // From ushort to int, uint, long, ulong, float, double
        if (target_type == TypeManager.int32_type)
            return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);

The ushort_type above is cached in the TypeManager as follows:

public class Typemanager
    // cached unsigned short type
    static public Type ushort_type = typeof (System.UInt16);

One naive way of handling this is to remove all references to the unsigned types. I tried doing this snip, snip, snip ... and it's no fun but a plain drudgery.

Then I sat back and said to myself, sure enough, I can do better than this and ended up doing this -

namespace Mono.CSharp {
    public class NotDefinedAsPrimitiveType {

public class TypeManager
    public static Type ushort_type = typeof (NotDefinedAsPrimitiveType);

Barely three lines of change and most of the feature creep is gone !

Btw, I should admit that it took more time writing these few lines of code than doing all those snips ...

Coming back to the question that I raised previously, the obvious answer is that I should start educating myself about the language semantics in the C# world. This will help me make educated and intelligent choices for handling of feature creeps.


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