public override IExpr Build(BuildContext ctx, IExprBuilder initiator, Func <IExpr> next)
{
//
// `StringConcatExprBuilder` is an optimization for expressions that contains a `+` (plus),
// and at least one operand of a `String` type.
// String concatenations are also possible with objects of an `Any` type. Only that, those
// expressions are built as `MathExpr` (since there is no way, rather than identifying type at the runtime).
if (ctx.Token is ArithmeticSymbolToken t && t.Operation == Enums.ArithmeticOperation.Add)
{
if (initiator is StringConcatExprBuilder || ctx.BuiltExprs.Count == 0)
{
return(null);
}
var prevExpr = ctx.LastExpr;
if (prevExpr.ReturnType == Enums.Type.String)
{
ctx.NextIndex();
var nextExpr = next();
ThrowIfExprIsNull(nextExpr, t);
ctx.PopExpr();
return(new StringConcatExpr(Env)
{
Token = t, A = prevExpr, B = nextExpr,
});
}
else
{
if (!_applyOptimization) // try to find if B contains a string (has high computational cost)
{
var ctxCopy = ctx.CreateCopy();
ctx.NextIndex();
var nextExpr = next();
ThrowIfExprIsNull(nextExpr, t);
if (nextExpr.ReturnType == Enums.Type.String)
{
ctx.PopExpr();
return(new StringConcatExpr(Env)
{
Token = t, A = prevExpr, B = nextExpr,
});
}
ctx.RestoreFrom(ctxCopy);
}
}
}
return(null);
}