F# 文字/常量可以由字符串组成，但不能由 int 组成？

Question

为什么可以:

let [<Literal>] hi = "hi"
let [<Literal>] bye = "bye"
let [<Literal>] shortMeeting = hi + bye

……但这不是吗？

let [<Literal>] me = 1
let [<Literal>] you = 1
let [<Literal>] we = me + you

第三行给出了错误:

This is not a valid constant expression

那是怎么回事？

Answer 1

所以规范/文档有点不清楚，但提供了提示。

从规范(对于 F# 3.0):

A value that has the Literal attribute is subject to the following restrictions:

It may not be marked mutable or inline. It may not also have the ThreadStaticor ContextStatic attributes. The righthand side expression must be a literal constant expression that is made up of either:

A simple constant expression, with the exception of (), native integer literals, unsigned native integer literals, byte array literals, BigInteger literals, and user-defined numeric literals.

OR

A reference to another literal

这似乎表明，即使是字符串的组合也是不允许的。

文档指出，这在 F# 3.1 中发生了变化:

https://msdn.microsoft.com/en-us/library/dd233193.aspx

As of F# 3.1, you can use the + sign to combine string literals. You can also use the bitwise or (|||) operator to combine enum flags. For example, the following code is legal in F# 3.1:

请注意，整数加法不在该列表中