## SoapFormatter cannot deserialize Hashtable and similar ordered collection objects

### Scope
Minor

### Version Introduced
4.5

### Source Analyzer Status
Available

### Change Description

The <xref:System.Runtime.Serialization.Formatters.Soap.SoapFormatter?displayProperty=name>
does not guarantee that objects serialized under one .NET Framework version will
successfully deserialize under a different version. Specifically, some ordered
collections (like <xref:System.Collections.Hashtable?displayProperty=name>)
added members between 4.0 and 4.5 such that objects of these types cannot
deserialize with .NET 4.0 if they were serialzied with .NET 4.5. Note that if
the serialized data is both serialized and deserialized with the same .NET
Framework version, no issue will occur.

- [ ] Quirked
- [ ] Build-time break

### Recommended Action

<xref:System.Runtime.Serialization.Formatters.Soap.SoapFormatter?displayProperty=name>
serialization should be replaced with
<xref:System.Runtime.Serialization.Formatters.Binary.BinaryFormatter?displayProperty=name>
serialization or <xref:System.Runtime.Serialization.NetDataContractSerializer?displayProperty=name>
to be resilient to .NET Framework changes.

### Affected APIs
* `M:System.Runtime.Serialization.Formatters.Soap.SoapFormatter.Serialize(System.IO.Stream,System.Object)`
* `M:System.Runtime.Serialization.Formatters.Soap.SoapFormatter.Serialize(System.IO.Stream,System.Object,System.Runtime.Remoting.Messaging.Header[])`
* `M:System.Runtime.Serialization.Formatters.Soap.SoapFormatter.Deserialize(System.IO.Stream)`
* `M:System.Runtime.Serialization.Formatters.Soap.SoapFormatter.Deserialize(System.IO.Stream,System.Runtime.Remoting.Messaging.HeaderHandler)`

### Category
Serialization

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