为什么我可以用[pscustomobject]而不是[System.Management.Automation.PSCustomObject]？来创建对象？

Question

为什么我可以用类型加速器pscustomobject而不是它的全名System.Management.Automation.PSCustomObject创建对象呢？有什么神奇的构造函数我没有访问吗？

$a = [pscustomobject]@{name='joe'}
$a.gettype().fullname
System.Management.Automation.PSCustomObject

[System.Management.Automation.PSCustomObject]@{name='joe'}
InvalidArgument: Cannot convert the "System.Collections.Hashtable" value of type "System.Collections.Hashtable" to type "System.Management.Automation.PSCustomObject".

或者我可以试试System.Management.Automation.PSObject，但我只得到了一个哈希表：

[psobject].Assembly.GetType('System.Management.Automation.TypeAccelerators')::get.pscustomobject.fullname
System.Management.Automation.PSObject

[System.Management.Automation.PSObject]@{name='joe'}                                                     

Name                           Value
----                           -----
name                           joe

受这个线程的启发：https://powershell.org/forums/topic/type-accelerator

Answer 1

，我没有访问什么神奇的构造函数吗？

不，编译器中有魔力--每当PowerShell编译器看到一个转换表达式，其中右边是字典，类型为pscustomobject时，它就会将字典或哈希表(无论是字面还是非文本)视为有序字典，并将其转换为PSObject。

来自VisitConvertExpression in Compiler.cs

var typeName = convertExpressionAst.Type.TypeName;
var hashTableAst = convertExpressionAst.Child as HashtableAst;
Expression childExpr = null;
if (hashTableAst != null)
{
    var temp = NewTemp(typeof(OrderedDictionary), "orderedDictionary");
    if (typeName.FullName.Equals(LanguagePrimitives.OrderedAttribute, StringComparison.OrdinalIgnoreCase))
    {
        return Expression.Block(
            typeof(OrderedDictionary),
            new[] { temp },
            BuildHashtable(hashTableAst.KeyValuePairs, temp, ordered: true));
    }

    if (typeName.FullName.Equals("PSCustomObject", StringComparison.OrdinalIgnoreCase))
    {
        // pure laziness here - we should construct the PSObject directly.  Instead, we're relying on the conversion
        // to create the PSObject from an OrderedDictionary.
        childExpr = Expression.Block(
            typeof(OrderedDictionary),
            new[] { temp },
            BuildHashtable(hashTableAst.KeyValuePairs, temp, ordered: true));
    }
}

请注意，这也是[ordered]@{Key='Value'}如何产生OrderedDictionary的