Thread by @vcsjones

TIL: C# has a `strict` option.

Next thing you know, it'll have an Explicit and On Error feature option too.

So I had a look at all the neat things this flag does. First, without the flag, this does not emit any error at all.

lock (null)
{
}

with strict, this no longer compiles. (1/n tweets)

Currently C# lets you use is/as against a static class. Strict prevents it. This compiles without the flag. (2/n)

static class Foo {
static void Bar(object baz) {
if (baz is Foo) {
}
}
}

C# without "strict" will let you do a null check against Guid or IntPtr even though they're structs and not emit a warning. With the strict feature, it emits a warning like other struct types. (3/n)

Guid baz = Guid.NewGuid();
if (baz == null) { // Produces warning with strict
}

Strict prevents this from compiling, which compiles with no errors or warnings by default.

enum Cat { Fuchsia, White }
static void Bar() {
var foo = 1 - Cat.Fuchsia;
Console.WriteLine(foo);
}

C# lets you pass arguments to a delegate's constructor by ref. `strict` prevents that from compiling. (5/n)

var v = new Func<string, string>(x => x);
var y = new Func<string, string>(ref v); //Does not compile with Strict

FOR THE RECORD, the Roslyn (C#) team does _not_ "support" this flag. I do not recommend you shove it in all your project files now. I just find it interesting that they _have_ fixed several bugs, and have the fixes gated behind something unsupported.