C# learning record: Writing high-quality code and improving organization suggestions 4-8

4. TryParse is better than Parse

The following TryParse method definition

public static bool TryParse(string s, out Double result);

Parse will report an error if the conversion fails, but TryParse has a return value. Determine whether the conversion is successful

string str1 = "abfc12";
if(double.TryParse(str1, out double dou1))
{
    Console.WriteLine(dou1);
}

5. It is recommended to use int? to ensure that the value type can also be null

If the value type needs to be null, we may use a special value such as -1 to To determine whether int is empty, it is best to change it to int? Type, determine whether it is null

Nullable<int> i1 = 4;
// i2 和 i1 的定义方式一样 只是写法不同 下面的int?是一个语法糖
int? i2 = null;
int i3 = 0;
//int类型可以默认转为int？类型
i2 = i3;
//int？类型需要强转成int类型，如果是null则变为0
i3 = (int)i2;

6. How to use readonly and const

The simple difference is that const is more efficient and readonly is more flexible

const is a compiler constant , readonly is a runtime constant

const int constNum = 1;
public string name;
public int age;
public FirstType()
{
    name = "aa";
    age = constNum;
    age = 1;
}
//使用以上代码测试，下面的编译成的IL代码
  IL_0000:  ldarg.0
  IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
  IL_0006:  nop
  IL_0007:  nop
  IL_0008:  ldarg.0
  IL_0009:  ldstr      "aa"
  IL_000e:  stfld      string CSharpSuggest.FirstType::name
  IL_0013:  ldarg.0
  IL_0014:  ldc.i4.1
  IL_0015:  stfld      int32 CSharpSuggest.FirstType::age
  IL_001a:  ldarg.0
  IL_001b:  ldc.i4.1
  IL_001c:  stfld      int32 CSharpSuggest.FirstType::age
  IL_0021:  ret

It can be seen that 13, 14, 15 are the same as 1a, 1b, 1c, so age = constNum; and age = 1; are equivalent and therefore the most efficient

const can only modify primitive types, enumeration types or string types, readonly has no restrictions

const is naturally static and cannot be added to static

The value of readonly is generally in the construction When assigning values ​​in the function, each class object can have a different readonly value, but since const is static, the value is the same for all classes

Book In the above sentence, I have always had a question, what is the difference between assignment in the class and assignment in the constructor? I can't find it online. The decompiled IL code is only the difference in the order of variable definition. If you know, please let me know. .

7. Use 0 as the default value of the enumeration

What I understand is that if it is not necessary, do not change the value of the enumeration, as unexpected results may occur

8. Avoid providing displayed values ​​for enumeration type elements

The reasons are the same as above

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