Wednesday, 21 June 2017

A Distaste For Expression Bodied Members

I really like to see programming languages evolve, getting new features version after version. Even if some of those features are not particularly useful or revolutionary, but just a way to make code less verbose, I appreciate them, as I like to see evolution and dynamism, being forced to learn something new. Microsoft has put quite a bit of effort in saving us to type repetitive code and do our code more concise. The introduction of Automatic properties was a huge step, and the improvements done in the last versions (default values for Automatic properties, read only auto properties, and both features combined) are pretty sweet.

//Automatic property with default value
public string FavoriteCity {get; set;} = "Paris";

//Read Only Automatic property (I'll be setting its value in the constructor
public string BirthCity {get;}
//Read Only Automatic property with default value
public DateTime BirthDate {get;} = DateTime.Now;

Another "big feature" in terms of type strokes saving has been Expression Bodied Mmembers. Honestly, this feature feels like a bit irritating to me.

So now you can write a method like this:

public int FormatString(string st) => $"---{st}---";

//rather than like this:
public int FormatString(string st){
return $"---{st}---";

I don't see it particularly helpful, but guess others will find it cool. The problem for me comes when we use it with Automatic Properties. Let's see:

public string FrenchFullName => $"{this.LastName.ToUpper()}, {this.Name}";

//is equivalent to:
public string FrenchFullName 
 get{ return $"{this.LastName.ToUpper()}, {this.Name}";}


//And here an identical method

public string GetFrenchFullName() => $"{this.LastName.ToUpper()}, {this.Name}";

So in the first line I have a property and in the last line a method. At first sight it's not easy to see if it's a method or a property, the only difference is the extra "()". If you follow the correct nomenclature, properties should be nouns and methods should be verbs, there's no room for confusion, but anyway, I feel a bit uneasy with this similarity.

Furthermore, this syntax can be applied to create local functions (added in C# 7). So you can write alocal function in any of these 2 ways:

public static void InternalFunctionTest()
   string applyFormat(int num){
    return $"[{num.ToString()}]";
   string applyFormat1(int num) =>  $"[{num.ToString()}]";

If you use the second way, it looks a bit similar to what we would have done in the past if we wanted to avoid polluting the class with a function that is only used from a certain method, write it as a lambda:

Func<int, string> applyFormat2 = (int num) => $"[{num.ToString()}]";

Under the covers, this is quite different from the expression bodied local function. In this case we are creating a new object, a delegate, while with the local function such object creation is not needed. There are more differences in terms on where the compiler creates the underlying method and the use of closures, but I've read some contradictory informations about this, so I'll have to spend some time to get the complete idea.

The "=>" syntax has been a pretty bad choice in my opinion and probably the source for my distaste for Expression Bodied Members . It's linked in my mind to delegates, so it takes my brain some extra cycles to break that association each time I see this symbol.

No comments:

Post a Comment