Explain Linq Query in C#

Question

Hello,

I understand the below query.

      static bool isUppercase(string s)
        {
            return s.All(x=> char.IsUpper(x));
        }

But I don't understand the following:

            static bool isUppercase(string s)
            {
                  return s.All(char.IsUpper); //It's a little confusing.
            }

Answer 1

Hi @Shervan360 ,

s.All(char.IsUpper);

Take a look at:

1. What is a method group in C#?
2. C# method group strangeness

Hope them could be helpful.

Best Regards,
Xingyu Zhao
*
If the answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Answer 2

Look at Intellisense and then look at the docs Char.IsUpper

I would make this an extension method

public static class StringExtensions  
{  
    public static bool IsUppercase(this string s) => s.All(char.IsUpper);  
}  

Then write a test method

[TestMethod]  
public void IsAllTest()  
{  
    var name = "karen";  
    Assert.IsFalse(name.IsUppercase());  
  
    name = "KAREN";  
    Assert.AreEqual(name, "KAREN");  
}  

This might make more sense

public static class StringExtensions  
{  
    public static bool IsUppercase(this string source) => source.All(char.IsUpper);  
    public static bool IsUpperCase(this string source) => (from character in source where char.IsUpper(character) select character).Count() == source.Length;  
}  


[TestMethod]  
public void IsAllTest()  
{  
    var name = "karen";  
    Assert.IsFalse(name.IsUpperCase());  
  
    name = "KAREN";  
    Assert.IsTrue(name.IsUpperCase());  
}  

Then back to this which uses a method group and is harder for novice developers to grasp

[DebuggerStepThrough]  
public static bool IsUpperCase(this string source) =>   
    (source.Where(char.IsUpper)).Count() == source.Length;  

Answer 3

It’s really pretty simple. While you can pass a lambda in a linq expression you can also just pass a function that takes the correct argument type:

static bool IsUpper(char c)
{
      return char.IsUpper(c);
}

static bool isUppercase(string s)
{
     return s.All(IsUpper);
}

But there is no need to write the first method because char.ToUpper has the same signature.