Make wxBasicString as simple and safe to use as possible

Don't try to write a general purpose class, but provide just the methods
that we need in our code.

This fixes the bug added in 294436c8bb
which resulted in a crash because a literal string, not a BSTR, was
passed to wxBasicString ctor.

include/wx/msw/ole/oleutils.h

@@ -66,24 +66,26 @@ inline void wxOleUninitialize()
 class WXDLLIMPEXP_CORE wxBasicString
 {
 public:
-    // Takes over the ownership of bstr
-    explicit wxBasicString(BSTR bstr = NULL);
+    // Constructs with the owned BSTR set to NULL
+    wxBasicString() : m_bstrBuf(NULL) {}
 
-    // Constructs the BSTR from wxString
-    wxBasicString(const wxString& str);
+    // Constructs with the owned BSTR created from a wxString
+    wxBasicString(const wxString& str)
+        : m_bstrBuf(SysAllocString(str.wc_str(*wxConvCurrent))) {}
 
-    // Creates a copy of the BSTR owned by bstr
-    wxBasicString(const wxBasicString& bstr);
+    // Constructs with the owned BSTR as a copy of the BSTR owned by bstr
+    wxBasicString(const wxBasicString& bstr) : m_bstrBuf(bstr.Copy()) {}
 
     // Frees the owned BSTR
-    ~wxBasicString();
+    ~wxBasicString() { SysFreeString(m_bstrBuf); }
 
-    // Returns the owned BSTR and gives up its ownership
+    // Creates the owned BSTR from a wxString
+    void AssignFromString(const wxString& str);
+
+    // Returns the owned BSTR and gives up its ownership,
+    // the caller is responsible for freeing it
     BSTR Detach();
 
-    // Frees the owned BSTR
-    void Free();
-
     // Returns a copy of the owned BSTR,
     // the caller is responsible for freeing it
     BSTR Copy() const { return SysAllocString(m_bstrBuf); }
@@ -95,12 +97,6 @@ public:
     // Sets its BSTR to a copy of the BSTR owned by bstr
     wxBasicString& operator=(const wxBasicString& bstr);
 
-    // Creates its BSTR from wxString
-    wxBasicString& operator=(const wxString& str);
-
-    // Takes over the ownership of bstr
-    wxBasicString& operator=(BSTR bstr);
-
     /// Returns the owned BSTR while keeping its ownership
     operator BSTR() const { return m_bstrBuf; }
 

src/msw/ole/automtn.cpp

@@ -130,8 +130,8 @@ bool wxAutomationObject::Invoke(const wxString& member, int action,
     }
 
     int namedArgStringCount = namedArgCount + 1;
-    wxVector<wxBasicString> argNames(namedArgStringCount, wxString());
-    argNames[0] = member;
+    wxVector<wxBasicString> argNames(namedArgStringCount);
+    argNames[0].AssignFromString(member);
 
     // Note that arguments are specified in reverse order
     // (all totally logical; hey, we're dealing with OLE here.)
@@ -141,7 +141,7 @@ bool wxAutomationObject::Invoke(const wxString& member, int action,
     {
         if ( !INVOKEARG(i).GetName().empty() )
         {
-            argNames[(namedArgCount-j)] = INVOKEARG(i).GetName();
+            argNames[(namedArgCount-j)].AssignFromString(INVOKEARG(i).GetName());
             j ++;
         }
     }

src/msw/ole/oleutils.cpp

@@ -70,25 +70,10 @@ WXDLLEXPORT wxString wxConvertStringFromOle(BSTR bStr)
 // ----------------------------------------------------------------------------
 // wxBasicString
 // ----------------------------------------------------------------------------
-
-wxBasicString::wxBasicString(BSTR bstr)
-{
-    m_bstrBuf = bstr;
-}
-
-wxBasicString::wxBasicString(const wxString& str)
-{
-    m_bstrBuf = SysAllocString(str.wc_str(*wxConvCurrent));
-}
-
-wxBasicString::wxBasicString(const wxBasicString& bstr)
-{
-    m_bstrBuf = bstr.Copy();
-}
-
-wxBasicString::~wxBasicString()
+void wxBasicString::AssignFromString(const wxString& str)
 {
     SysFreeString(m_bstrBuf);
+    m_bstrBuf = SysAllocString(str.wc_str(*wxConvCurrent));
 }
 
 BSTR wxBasicString::Detach()
@@ -100,12 +85,6 @@ BSTR wxBasicString::Detach()
     return bstr;
 }
 
-void wxBasicString::Free()
-{
-    SysFreeString(m_bstrBuf);
-    m_bstrBuf = NULL;
-}
-
 BSTR* wxBasicString::ByRef()
 {
     wxASSERT_MSG(!m_bstrBuf,
@@ -126,25 +105,6 @@ wxBasicString& wxBasicString::operator=(const wxBasicString& src)
     return *this;
 }
 
-wxBasicString& wxBasicString::operator=(const wxString& str)
-{
-    SysFreeString(m_bstrBuf);
-    m_bstrBuf = SysAllocString(str.wc_str(*wxConvCurrent));
-
-    return *this;
-}
-
-wxBasicString& wxBasicString::operator=(BSTR bstr)
-{
-    wxCHECK_MSG(m_bstrBuf == NULL || m_bstrBuf != bstr, 
-        *this, wxS("Attempting to assign already owned BSTR"));
-
-    SysFreeString(m_bstrBuf);
-    m_bstrBuf = bstr;
-
-    return *this;
-}
-
 // ----------------------------------------------------------------------------
 // Convert variants
 // ----------------------------------------------------------------------------