Why is it a memory ERRO.

[Dsby via Digitalmars-d-learn]

On Friday, 29 January 2016 at 12:43:53 UTC, Dsby wrote:
> the Code:
> class MyClass
> {
> 	this(){
> 		by = new ubyte[10000];
> 		++i;
> 	}
> 	~this(){
> 		GC.free(by.ptr);
> 		by = null;
> 		writeln("free");
> 	}
> 	void show(){
> 		writeln(i);
> 	};
> private:
> 	ubyte[]   by;
> 	static i = 0;
> };
>
> void main()
> {
> 	bool start = true;
> 	int i = 0;
> 	while(start){
> 		auto obj = new MyClass();
> 		obj.show();
> 		Thread.sleep(5.msecs);
> 		//obj.destroy;
> 		//GC.free(cast(void *)obj);
> 		++i;
> 		if (i > 20000)
> 			break;
> 	}
> }
>
> the code will be :
> 341
> core.exception.InvalidMemoryOperationError at src/core/exception.d(679): Invalid memory operation
> ----------------
> core.exception.InvalidMemoryOperationError at src/core/exception.d(679): Invalid memory operation
> ----------------
>
> .why is it?
> if < obj.destroy; > is exec. the code will not errno.

I am in 2.069, on opensuse leap 42.1 X86_64
dmd -v
DMD64 D Compiler v2.069
Copyright (c) 1999-2015 by Digital Mars written by Walter Bright