C# 7.1’s default value expressions enhancement: default literal expressions
For using C# 7.1, set Language Version to “C# latest minor version(latest)” or “C# 7.1” in C# project (Advanced Build Settings):
default literal expressions and type inference in C# 7.1
default literal can be used when type of the expression can be inferred. It can be used in:
variable initialisation & assignment
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public bool HasValue(string value, out string errorMessage) { errorMessage = default; // Some code. } |
optional parameter – default value declaring
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public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key, TValue defaultVaule = default) { // Some code. } |
method call argument
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public IEnumerable<Book> GetAllInStockBooks() => GetBooksAvailableForDisplay(default); public IEnumerable<Book> GetBooksAvailableForDisplay(Func<Book, bool> validate) { // Some code. } |
return statement
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public static T GetValueOrDefault<T>(this IDataRecord row, string fieldName) { // Some Code. if (row.IsDBNull(ordinal)) { return default; } // Some Code. } |
Full sample code to explain the use of default value expressions in older versions of C# (before C# 7.1)
Note the use of default value expressions:
- variable initialisation & assignment (errorMessage = default(string) )
- optional parameter – default value declaring (TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key, TValue defaultVaule = default(TValue)))
- method call argument (GetBooksAvailableForDisplay(default(Func<Book, bool>)))
- return statement (return default(T))
in the below sample code:
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/// <summary> /// Dictionary Extentions. /// </summary> public static class DictionaryExtentions { /// <summary> /// Get Value Or Default. /// </summary> /// <typeparam name="TKey">Type Param.</typeparam> /// <typeparam name="TValue">Type Param.</typeparam> /// <param name="dict">Dictionary.</param> /// <param name="key">Key.</param> /// <param name="defaultVaule">Default value to use.</param> /// <returns>Value.</returns> public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key, TValue defaultVaule = default(TValue)) { // value will be the result or the default for TValue TValue result; if (dict.TryGetValue(key, out result) == false) { result = defaultVaule; } return result; } } /// <summary> /// DataReader Extentions. /// </summary> public static class DataReaderExtentions { /// <summary> /// Get Value Or Default. /// </summary> /// <typeparam name="T">Type Param.</typeparam> /// <param name="row">DataReader row.</param> /// <param name="fieldName">Field Name.</param> /// <returns></returns> public static T GetValueOrDefault<T>(this IDataRecord row, string fieldName) { int ordinal = row.GetOrdinal(fieldName); if (row.IsDBNull(ordinal)) { return default(T); } return (T)row.GetValue(ordinal); } } /// <summary> /// CSharp Samples. /// </summary> public class CSharp { /// <summary> /// Input string has value or not. /// </summary> /// <param name="value">Input string.</param> /// <param name="errorMessage">Error Message (out parameter).</param> /// <returns>true or false.</returns> public bool HasValue(string value, out string errorMessage) { errorMessage = default(string); if (value == null) { errorMessage = $"{nameof(value)} is null."; } else if (value.Equals(string.Empty)) { errorMessage = $"{nameof(value)} is empty."; } else if (value.Trim().Equals(string.Empty)) { errorMessage = $"{nameof(value)} contains only whitespaces."; } return string.IsNullOrEmpty(errorMessage); } /// <summary> /// Get all in stock books. /// </summary> /// <returns></returns> public IEnumerable<Book> GetAllInStockBooks() => GetBooksAvailableForDisplay(default(Func<Book, bool>)); /// <summary> /// Books available for display. /// </summary> /// <param name="validate">Validate function.</param> /// <returns>Valid books for display.</returns> public IEnumerable<Book> GetBooksAvailableForDisplay(Func<Book, bool> validate) { IEnumerable<Book> booksAvailableInStock = GetBooks().Where(x => x.InStock); if (validate == null) { return booksAvailableInStock; } return booksAvailableInStock.Where(x => validate(x)); } /// <summary> /// Is valid book for display. /// </summary> /// <param name="book">Book.</param> /// <returns>Valid: true or false.</returns> public bool IsValidBookForDisplay(Book book) { if (book == null || string.IsNullOrWhiteSpace(book.Publisher) || string.IsNullOrWhiteSpace(book.BookCategory) || string.IsNullOrWhiteSpace(book.Title) || book.Id <= 0 || book.Price <= 0) { return false; } return true; } /// <summary> /// Get Books. /// </summary> private IEnumerable<Book> GetBooks() => new List<Book> { new Book { Publisher = "", BookCategory = "Web Development", Id = 1, Price = 450, Title = "Book1", InStock = false }, new Book { Publisher = "Apress", BookCategory = "Programming", Id = 2, Price = 250, Title = "Book2", InStock = true }, // valid new Book { Publisher = "wrox", BookCategory = "", Id = 3, Price = 499, Title = "Book3", InStock = true }, new Book { Publisher = "Apress", BookCategory = "Mobile", Id = 0, Price = 350, Title = "Book5", InStock = true }, new Book { Publisher = "wrox", BookCategory = "ASP.NET", Id = 6, Price = 485, Title = "Book6", InStock = false }, // valid new Book { Publisher = "Apress", BookCategory = "C#", Id = 7, Price = 0, Title = "Book7", InStock = false }, new Book { Publisher = "Apress", BookCategory = "C#", Id = 9, Price = 500, Title = "", InStock = true }, }; } /// <summary> /// Book Model. /// </summary> public class Book { public string Publisher { get; set; } public string BookCategory { get; set; } public int Id { get; set; } public string Title { get; set; } public decimal Price { get; set; } public bool InStock { get; set; } } |
Full sample code to explain the use of C# 7.1’s default literal expressions
Note the use of default literal expressions:
- variable initialisation & assignment (errorMessage = default )
- optional parameter – default value declaring (TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key, TValue defaultVaule = default))
- method call argument (GetBooksAvailableForDisplay(default))
- return statement (return default)
in the below sample code:
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/// <summary> /// Dictionary Extentions. /// </summary> public static class DictionaryExtentions { /// <summary> /// Get Value Or Default. /// </summary> /// <typeparam name="TKey">Type Param.</typeparam> /// <typeparam name="TValue">Type Param.</typeparam> /// <param name="dict">Dictionary.</param> /// <param name="key">Key.</param> /// <param name="defaultVaule">Default value to use.</param> /// <returns>Value.</returns> public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key, TValue defaultVaule = default) { // value will be the result or the default for TValue if (dict.TryGetValue(key, out TValue result) == false) { result = defaultVaule; } return result; } } /// <summary> /// DataReader Extentions. /// </summary> public static class DataReaderExtentions { /// <summary> /// Get Value Or Default. /// </summary> /// <typeparam name="T">Type Param.</typeparam> /// <param name="row">DataReader row.</param> /// <param name="fieldName">Field Name.</param> /// <returns></returns> public static T GetValueOrDefault<T>(this IDataRecord row, string fieldName) { int ordinal = row.GetOrdinal(fieldName); if (row.IsDBNull(ordinal)) { return default; } return (T)row.GetValue(ordinal); } } /// <summary> /// CSharp7_1 Samples. /// </summary> public class CSharp7_1 { /// <summary> /// Input string has value or not. /// </summary> /// <param name="value">Input string.</param> /// <param name="errorMessage">Error Message (out parameter).</param> /// <returns>true or false.</returns> public bool HasValue(string value, out string errorMessage) { errorMessage = default; if (value == null) { errorMessage = $"{nameof(value)} is null."; } else if (value.Equals(string.Empty)) { errorMessage = $"{nameof(value)} is empty."; } else if (value.Trim().Equals(string.Empty)) { errorMessage = $"{nameof(value)} contains only whitespaces."; } return string.IsNullOrEmpty(errorMessage); } /// <summary> /// Get all in stock books. /// </summary> /// <returns></returns> public IEnumerable<Book> GetAllInStockBooks() => GetBooksAvailableForDisplay(default); /// <summary> /// Books available for display. /// </summary> /// <param name="validate">Validate function.</param> /// <returns>Valid books for display.</returns> public IEnumerable<Book> GetBooksAvailableForDisplay(Func<Book, bool> validate) { IEnumerable<Book> booksAvailableInStock = GetBooks().Where(x => x.InStock); if (validate == null) { return booksAvailableInStock; } return booksAvailableInStock.Where(x => validate(x)); } /// <summary> /// Is valid book for display. /// </summary> /// <param name="book">Book.</param> /// <returns>Valid: true or false.</returns> public bool IsValidBookForDisplay(Book book) { if (book == null || string.IsNullOrWhiteSpace(book.Publisher) || string.IsNullOrWhiteSpace(book.BookCategory) || string.IsNullOrWhiteSpace(book.Title) || book.Id <= 0 || book.Price <= 0) { return false; } return true; } /// <summary> /// Get Books. /// </summary> private IEnumerable<Book> GetBooks() => new List<Book> { new Book { Publisher = "", BookCategory = "Web Development", Id = 1, Price = 450, Title = "Book1", InStock = false }, new Book { Publisher = "Apress", BookCategory = "Programming", Id = 2, Price = 250, Title = "Book2", InStock = true }, // valid new Book { Publisher = "wrox", BookCategory = "", Id = 3, Price = 499, Title = "Book3", InStock = true }, new Book { Publisher = "Apress", BookCategory = "Mobile", Id = 0, Price = 350, Title = "Book5", InStock = true }, new Book { Publisher = "wrox", BookCategory = "ASP.NET", Id = 6, Price = 485, Title = "Book6", InStock = false }, // valid new Book { Publisher = "Apress", BookCategory = "C#", Id = 7, Price = 0, Title = "Book7", InStock = false }, new Book { Publisher = "Apress", BookCategory = "C#", Id = 9, Price = 500, Title = "", InStock = true }, }; } /// <summary> /// Book Model. /// </summary> public class Book { public string Publisher { get; set; } public string BookCategory { get; set; } public int Id { get; set; } public string Title { get; set; } public decimal Price { get; set; } public bool InStock { get; set; } } |
Happy Coding !!!
