[数据类型]和[数据类型[]]之间的区别

Question

When casting a datatype for a variable, what does the extra empty square brackets do?

For example, in defining a parameter for a function, I have noticed these two ways of casting a data type for that parameter:

param(
    [string]$computername
)

vs:

param(
    [string[]]$computername
)

What purpose does the empty square brackets in the second example serve?

Answer 1

The parameter in the second example accepts a list of strings (an array), the parameter in the first example only a single string.

This works in both cases:

-computername 'foo'

This works just in the second case:

-computername 'foo', 'bar'

Answer 2

[] denotes an array. So [string[]]$computername would denote a string array of computername's.