| Constant | ReadOnly |
| می‌تواند به Fieldها و همچنین localها اعمال شود. | تنها به Field ها اعمال می‌شود. |
| مقدار دهی اولیه آن الزامی است. | مقدار دهی اولیه می‌تواند هنگام تعریف و یا در درون سازنده انجام شود (در هیچ متد دیگری امکان پذیر نیست). |
| تخصیص حافظه انجام نمی‌شود و مقدار آن در کدهای IL گنجانده می‌شود (توضیح در ادامه مطلب). | تخصیص حافظه بصورت داینامیک انجام می‌شود و می‌توانیم در زمان اجرا مقدار آن را بدست آوریم. |
| ثابت‌ها در #C بصورت پیش فرض از نوع static هستند. بدین معنا که از طریق نام کلاس قابل دسترسی هستند. | تنها از طریق وهله سازی از یک کلاس قابل دسترسی هستند. |
| نوع‌های درون ساز (built in) و Null Reference ها را می‌توان بصورت const تعریف کرد. Boolean,Char, Byte, SByte, Int16, UInt16, Int32, UInt32, Int64, UInt64, Single, Double, Decimal , string. | مشابه Constant ها |
| مقدار آن در طول عمر یک برنامه ثابت است. | مقدار آن می‌تواند در هنگام فراخوانی سازنده برای وهله‌های مختلف متفاوت باشد. |
| فیلدهای const را نمی‌توان بصورت پارامتر‌های out و ref استفاده کرد. | فیلدهای ReadOnly را می‌توان بصورت پارامتر‌های ref و out در درون سازنده استفاده کرد. |
const int field_constant = 10; //constant field
static void Main(string[] args)
{
const int x = 10, y = 15; //constant local :correct
const int z = x + y; //constant local : correct;
const int a = x + GetVariableValue();//Error
}
public static int GetVariableValue()
{
const int localx = 10;
return 10;
} 
class Program
{
public const int numberOfDays = 7;
public readonly double piValue = 3.14;
static void Main(string[] args)
{
}
} 
public const int numberOfDays = 7; public readonly double piValue = 3.14;
static void Main(string[] args)
{
var readEx = new MyLib.TestClass();
var readConstValue = MyLib.TestClass.numberOfDays;
var readReadOnlyValue = readEx.piValue;
} .method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint
// Code size 17 (0x11)
.maxstack 1
.locals init ([0] class [MyLib]MyLib.TestClass readEx,
[1] int32 readConstValue,
[2] float64 readOnlyValue)
IL_0000: nop
IL_0001: newobj instance void [MyLib]MyLib.TestClass::.ctor()
IL_0006: stloc.0 //readEx
IL_0007: ldc.i4.7 //ارزش ذخیره شده در کد
IL_0008: stloc.1 //readConstValue
IL_0009: ldloc.0 //readEg
IL_000a: ldfld float64 [MyLib]MyLib.TestClass::piValue
IL_000f: stloc.2 //readReadOnlyValue
IL_0010: ret
} // end of method Program::Main public class ReadonlyStatic
{
public static readonly string x = "Hi";
public static readonly string y;
public ReadonlyStatic()
{
//y = "Hello"; This is wrong
}
static ReadonlyStatic()
{
y = "Hello";
}
} | ReadOnly | Static |
| هم در زمان تعریف و هم از طریق سازنده می‌توان آن را مقدار دهی کرد. | در زمان تعریف و تنها از طریق سازنده static می‌توان آن را مقدار دهی کرد. |
| مقدار بر اساس مقادیری که در سازنده‌ها تعیین می‌شود متفاوت است. | مقادیر بعد از مقدار دهی اولیه تغییر نمی‌کنند. |
چه زمانی از Const و چه زمانی از ReadOnly استفاده کنیم :
We have a long, complex, difficult to understand method that is extremely hard to refactor under these circumstances. And that’s just looking at the mutability smells in code.
const columns = [
{
field: "fullname",
headerName: "First & last Name",
description: "name of user",
width: 50,
},
{
field: "age",
headerName: "Age",
description: "age of user",
width: 50,
renderCell:(info)=><strong>Age is : {info.data.age}</strong>
}
] ... const [rows,setRows] = useState([]); const [loading,setLoading] = useState(false); const [totalCount,setTotalCount] = useState(0);
const [filter,setFilter] = useState({ pageSize:10, pageNumber:1 });
const _fetchData = async () => { if (!active) return; //mock api, you can call your api then set data to table like commented line below return new Promise((resolve) => { setLoading(true); setTimeout(() => { setRows(data);// SetRows, note that data comes from api and must be array of objects setTotalCount(7);//=== set total page size for pagination part resolve(); setLoading(false); }, 2000); }); }
import Angrid from "rect-angrid";
...
_handlePageChange = (newPage)=>{
setFilter(p=>({...p,pageNumber:newPage}))
}
...
<AnGrid
loading={loading}
columns={columns}
rows={rows}
showRowNumber={true}
pageSize={filter.pageSize}
pageNumber={filter.pageNumber}
totalCount={totalCount}
onPageChange={_handlePageChange}
theme="dark"
minHeight={300}
emptyList={<strong>There Is No Info</strong>}
/> 
Originally developed at Google, gRPC today is a remote procedure call (RPC) framework that has emerged as an alternative to RESTful and HTTP-based interfaces to connect remote components and specifically microservices. The new RPC framework was created in part to work with modern technologies such as HTTP/2 and Protobuf.
use master; RESTORE DATABASE WideWorldImporters FROM disk='D:\path\WideWorldImporters-Full.bak' WITH MOVE 'WWI_Primary' TO 'D:\SQL_Data\WideWorldImporters.mdf', MOVE 'WWI_Log' TO 'D:\SQL_Data\WideWorldImporters_log.ldf', MOVE 'WWI_UserData' TO 'D:\SQL_Data\WideWorldImporters_UserData.ndf', MOVE 'WWI_InMemory_Data_1' TO 'D:\SQL_Data\WideWorldImporters_InMemory_Data_1'
USE [WideWorldImporters];
GO
SELECT
[s].[StateProvinceName],
[s].[SalesTerritory],
[s].[LatestRecordedPopulation],
[s].[StateProvinceCode]
FROM [Application].[Countries] [c]
JOIN [Application].[StateProvinces] [s]
ON [s].[CountryID] = [c].[CountryID]
WHERE [c].[CountryName] = 'United States';
GO 
USE [WideWorldImporters];
GO
SET STATISTICS IO ON;
GO
SET STATISTICS TIME ON;
GO
SELECT
[s].[StateProvinceName],
[s].[SalesTerritory],
[s].[LatestRecordedPopulation],
[s].[StateProvinceCode]
FROM [Application].[Countries] [c]
JOIN [Application].[StateProvinces] [s]
ON [s].[CountryID] = [c].[CountryID]
WHERE [c].[CountryName] = 'United States';
GO SQL Server parse and compile time: CPU time = 0 ms, elapsed time = 504 ms. (53 rows affected) Table 'Countries'. Scan count 0, logical reads 118, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'StateProvinces'. Scan count 1, logical reads 43, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times: CPU time = 0 ms, elapsed time = 10 ms.
USE [WideWorldImporters];
GO
SET STATISTICS XML ON;
GO
SELECT
[s].[StateProvinceName],
[s].[SalesTerritory],
[s].[LatestRecordedPopulation],
[s].[StateProvinceCode]
FROM [Application].[Countries] [c]
JOIN [Application].[StateProvinces] [s]
ON [s].[CountryID] = [c].[CountryID]
WHERE [c].[CountryName] = 'United States';
GO
SET STATISTICS XML OFF;
GO SQL Server parse and compile time: CPU time = 0 ms, elapsed time = 0 ms. SQL Server Execution Times: CPU time = 0 ms, elapsed time = 0 ms. SQL Server parse and compile time: CPU time = 0 ms, elapsed time = 0 ms. SQL Server Execution Times: CPU time = 0 ms, elapsed time = 0 ms. SQL Server parse and compile time: CPU time = 0 ms, elapsed time = 7 ms. (53 rows affected) Table 'Countries'. Scan count 0, logical reads 118, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'StateProvinces'. Scan count 1, logical reads 43, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. (1 row affected) SQL Server Execution Times: CPU time = 15 ms, elapsed time = 179 ms. SQL Server parse and compile time: CPU time = 0 ms, elapsed time = 0 ms. SQL Server Execution Times: CPU time = 0 ms, elapsed time = 0 ms.
SET STATISTICS IO ON;
GO
SET STATISTICS TIME ON;
GO
SELECT
[s].[StateProvinceName],
[s].[SalesTerritory],
[s].[LatestRecordedPopulation],
[s].[StateProvinceCode]
FROM [Application].[Countries] [c]
JOIN [Application].[StateProvinces] [s]
ON [s].[CountryID] = [c].[CountryID]
WHERE [c].[CountryName] = 'United States';
GO 
USE [WideWorldImporters];
GO
SELECT
[s].[StateProvinceName],
[s].[SalesTerritory],
[s].[LatestRecordedPopulation],
[s].[StateProvinceCode]
FROM [Application].[Countries] [c]
JOIN [Application].[StateProvinces] [s]
ON [s].[CountryID] = [c].[CountryID]
WHERE [c].[CountryName] = 'United States';
GO 
USE [WideWorldImporters];
GO
SELECT
[s].[StateProvinceName],
[s].[SalesTerritory],
[s].[LatestRecordedPopulation],
[s].[StateProvinceCode]
FROM [Application].[Countries] [c]
JOIN [Application].[StateProvinces] [s]
ON [s].[CountryID] = [c].[CountryID]
WHERE [c].[CountryName] = 'United States';
GO 
SELECT
[s].[StateProvinceName],
[s].[SalesTerritory],
[s].[LatestRecordedPopulation],
[s].[StateProvinceCode]
FROM [Application].[Countries] [c]
JOIN [Application].[StateProvinces] [s]
ON [s].[CountryID] = [c].[CountryID]
WHERE [s].[StateProvinceName] LIKE 'O%';
GO 
I can tell at least that in 3 years, JavaScript will gain more the status of a VM and lose the status of a language. Already today, not many people use raw JavaScript. You usually have some transpilation, at least e.g. Babel. In the future, Web Assembly will enable more innovation in that regards, and existing transpiling languages like Elm, TypeScript, PureScript will continue to improve.
If you write copious amounts of CSS, a pre-processor can greatly decrease your stress levels and save you a lot of precious time. Using tools such as Sass, Less, Stylus or PostCSS makes large and complicated stylesheets clearer to understand and easier to maintain. Thanks to features like variables, functions and mixins the code becomes more organized, allowing developers to work quicker and make less mistakes.
