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Hello gurus,

First, I am resubmitting this question because of a misunderstanding I had about the Code Project sign-in. My apologies for any confusion this may cause.

In a previous post I had a problem which was neatly solved using partial function applications. Now I have a problem, not with the coding of the solution, but with trying to understand the syntax of the solution.

Background:
I have defined a set of Funcs which I use to validate data. An example is
Func<int, Func<object, string>> MaxLen => max => value => CheckLength(value, max);

which I use in a Dictionary that defines rules for various data fields in a file:
_rules = new FileRules()
{
{ "FH03", new FieldRules() { AlphaNumeric, MaxLen(10), ... } },
{ "FH04", new FieldRules() { AlphaNumeric, MaxLen(30), ... } },
...
};
I use it like this
object validated = stuffToOutput;
try
{
    foreach (var rule in _rules[fieldId])
    {
        validated = rule(validated);
    }
}
catch (Exception ex) { ... }

This allows me to pass in the data for field FH03 and have it checked to see that it is alphanumeric and has a maximum length of 10 characters, etc. This code works wonderfully, and I understand how it works. My problem is that I am struggling to express to others how it works. In particular, the proper terminology to use to describe definition of the partial function application in the syntax I am using.

Problem:
This page indicates that lambda expressions are interpreted as parameters on the left of the => and expression on the right. With that
value => CheckLength(value, max)

is easily explained as a lambda that takes a parameter called value and returns the result of CheckLength(value, max).
max => value => CheckLength(value, max)

is explained as a lambda that takes a parameter called max and returns the result of the lambda on the right.

But then I get to
Func<int, Func<object, string>> MaxLen => max => value => CheckLength(value, max)

In the lexicon of C#, what is MaxLen?

It is not a parameter - its usage in the first code block (where the dictionary entries are defined) is inconsistent with it being a parameter.

I thought it would make sense to say it is the name of a named delegate, but it does not match the syntactic signature of any delegate types shown on this MS page. All of those examples show
Delegate delegatename = delegatedefinition;

There is no = in the syntax I am using.

Even this reference, which shows the Action delegate type used with a lambda expression as the definition, uses the syntax
Action delegatename = parms => lambda-expression;


Is MaxLen a Func? Again this entry shows that Funcs are also expressed with equal signs
Func funcname = parms => lambda-expression;

Again, no equal sign in mine.

So, how would I word what MaxLen is? What is the proper terminology to describe it?

What I have tried:

Racking my brain
Scouring MS sites for terminology
Posted
Updated 16-Jan-19 16:36pm

1 solution

It's a read-only property. You could rewrite it like this:
C#
Func<int, Func<object, string>> MaxLen { get; } = max => value => CheckLength(value, max);
 
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Comments
C Pottinger 17-Jan-19 15:45pm    
Thank you, Graeme. That makes perfect sense as I look it now.

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