c# StringBuilder with Linq-ish capabilities IfElse is this possible?

Question

I'm writing down an AST (abstract syntax tree) not in tree form but with the intent of correctly formatting my code.. similar to Clang for a custom language and I'm using a StringBuilder for the effect... Right now I have to do things like:

        public string Visit(IfStatement ifStatement, int indent = 0)
        {
            var sb = new StringBuilder()
                .Append('\t', indent)
                .Append(Token.IfKeyword.ToString())
                .AppendBetween(ifStatement.Test.Accept(this), "(", ")").AppendLine()
                .Append(ifStatement.Consequent.Accept(this, indent + 1));

            if (ifStatement.Consequent != null)
            {
                sb.AppendLine()
                    .Append('\t', indent)
                    .AppendLine(Token.ElseKeyword.ToString())
                    .Append(ifStatement.Consequent.Accept(this, indent + 1));
            }

            return sb.ToString();
        }

This sometimes gets pretty complex so I was hoping I could do something like:

sb.Append("Hello").IfElse(a > 5, sb => sb.Append("world!"), sb => sb.AppendLine("ME!!")).Append(...)

Can this be done using class extensions? Thank you very much for your time!

(BTW is there a better way to write down an AST? I'm currently using the Visitor pattern for the effect but if you know a better way please let me know... I also wanted to introduce text wrapping if certain line width is reached.. don't know how to do that though).

`sb.Append("Hello").Append(a > 5 ? "world!" : "ME!!\n").Append(...)`? — GSerg, Dec 20 '19 at 21:35
@GSerg Probably should use `Environment.NewLine` instead of `\n`. — juharr, Dec 20 '19 at 21:38
In my example I use AppendBetween that adds start and end text if it doesn't exist yet. For example `sb.AppendBetween("Hello", "(", ")")` return '"(Hello)"' and `sb.AppendBetween("(Hello)", "(", ")")` also returns '"(Hello)"' the AppendLine was only to give a smaller example. What if I want to do something like `sb.Append("Hello").IfElse(a > 5, sb => sb.Append("world!"), sb => sb.AppendBetween("ME!!")).Append(...)` ? — xDGameStudios, Dec 20 '19 at 21:39
@juharr Yes, but that would be string concatenation which is weird in the context of using a stringbuilder, at which point I would rather implement an actual `IfElse` extension method. Which is pretty trivial as it's `public static StringBuilder IfElse(this StringBuilder sb, bool condition, Action if_true, Action if_false) { if (condition) { if_true(); } else { if_false(); } return sb; }`. — GSerg, Dec 20 '19 at 21:46
Alternatively, `public static StringBuilder IfElse(this StringBuilder sb, bool condition, Action if_true, Action if_false) { if (condition) { if_true(sb); } else { if_false(sb); } return sb; }`, if the idea is to pass `sb => sb.Append()` rather than `() => sb.Append()`. — GSerg, Dec 20 '19 at 21:51

score 0 · Answer 1 · answered Dec 21 '19 at 14:51

I ended up following @GSerg suggestion.

public static StringBuilder IfElse(this StringBuilder sb, bool condition, Action<StringBuilder> if_true, Action<StringBuilder> if_false) 
{ 
    if (condition) { if_true(sb); } else { if_false(sb); } return sb; 
}

and then I can do:

new StringBuilder().Append("World").IfElse(!IsNight(), sb => sb.Insert(0, "Hello ".AppendFormat(", my name is {0}", GetName())), sb => sb.Insert(0, "Bye "))

I just didn't know how the lambda thing sb => sb.Whatever() worked (I need to use functions as arguments).

c# StringBuilder with Linq-ish capabilities IfElse is this possible?

1 Answers1