C# 中的字符串内插

var date = new DateTime(1731, 11, 25);
Console.WriteLine($"On {date:dddd, MMMM dd, yyyy} Leonhard Euler introduced the letter e to denote
{Math.E:F5} in a letter to Christian Goldbach.");
// Expected output:
// On Sunday, November 25, 1731 Leonhard Euler introduced the letter e to denote 2.71828 in a letter to Christian Goldbach.

double a = 3;
double b = 4;
Console.WriteLine($"Area of the right triangle with legs of {a} and {b} is {0.5 * a * b}");
Console.WriteLine($"Length of the hypotenuse of the right triangle with legs of {a} and {b} is
{CalculateHypotenuse(a, b)}");
double CalculateHypotenuse(double leg1, double leg2) => Math.Sqrt(leg1 * leg1 + leg2 * leg2);
// Expected output:
// Area of the right triangle with legs of 3 and 4 is 6
// Length of the hypotenuse of the right triangle with legs of 3 and 4 is 5

一. 如何控制设置了格式的内插表达式的字段宽度和对齐方式

通过在内插表达式后添加逗号（“,”）和常数表达式来指定设置了格式的表达式结果的最小字段宽度和对齐方式：
{<interpolationExpression>,<alignment>}
如果对齐方式值为正，则设置了格式的表达式结果为右对齐，如果为负，则为左对齐。
如果需要同时指定对齐方式和格式字符串，则先从对齐方式组件开始：
{<interpolationExpression>,<alignment>:<formatString>}

示例演示

const int NameAlignment = -9;
const int ValueAlignment = 7;
double a = 3;
double b = 4;
Console.WriteLine($"Three classical Pythagorean means of {a} and {b}:");
Console.WriteLine($"|{"Arithmetic",NameAlignment}|{0.5 * (a + b),ValueAlignment:F3}|");
Console.WriteLine($"|{"Geometric",NameAlignment}|{Math.Sqrt(a * b),ValueAlignment:F3}|");
Console.WriteLine($"|{"Harmonic",NameAlignment}|{2 / (1 / a + 1 / b),ValueAlignment:F3}|");
// Expected output:
// Three classical Pythagorean means of 3 and 4:
// |Arithmetic| 3.500|
// |Geometric| 3.464|
// |Harmonic | 3.429|

 二. 如何在内插字符串中使用转义序列

var xs = new int[] { 1, 2, 7, 9 };
var ys = new int[] { 7, 9, 12 };
Console.WriteLine($"Find the intersection of the {{{string.Join(", ",xs)}}} and {{{string.Join(", ",ys)}}}
sets.");
var userName = "Jane";
var stringWithEscapes = $"C:\\Users\\{userName}\\Documents";
var verbatimInterpolated = $@"C:\Users\{userName}\Documents";
Console.WriteLine(stringWithEscapes);
Console.WriteLine(verbatimInterpolated);
// Expected output:
// Find the intersection of the {1, 2, 7, 9} and {7, 9, 12} sets.
// C:\Users\Jane\Documents
// C:\Users\Jane\Documents

三.如何在内插表达式中使用三元条件运算符 ?:

var rand = new Random();
for (int i = 0; i < 7; i++)
{
Console.WriteLine($"Coin flip: {(rand.NextDouble() < 0.5 ? "heads" : "tails")}");
}

四.如何使用字符串插值创建区域性特定的结果字符串

var cultures = new System.Globalization.CultureInfo[]
{
　　System.Globalization.CultureInfo.GetCultureInfo("en-US"),
　　System.Globalization.CultureInfo.GetCultureInfo("en-GB"),
　　System.Globalization.CultureInfo.GetCultureInfo("nl-NL"),
　　System.Globalization.CultureInfo.InvariantCulture
};
var date = DateTime.Now;
var number = 31_415_926.536;
FormattableString message = $"{date,20}{number,20:N3}";
foreach (var culture in cultures)
{
var cultureSpecificMessage = message.ToString(culture);
Console.WriteLine($"{culture.Name,-10}{cultureSpecificMessage}");
}
// Expected output is like:
// en-US 5/17/18 3:44:55 PM 31,415,926.536
// en-GB 17/05/2018 15:44:55 31,415,926.536
// nl-NL 17-05-18 15:44:55 31.415.926,536
// 05/17/2018 15:44:55 31,415,926.536

五,如何使用固定区域性创建结果字符串

string messageInInvariantCulture = FormattableString.Invariant($"Date and time in invariant culture:
{DateTime.Now}");
Console.WriteLine(messageInInvariantCulture);
// Expected output is like:
// Date and time in invariant culture: 05/17/2018 15:46:24