Nobody says that EX4 is launched on MT5. It's just that you can write advisors on MQL4, while having them run on MT5, not knowing the MQL5 at all.
Not without conversion functions.
The topic title is: Is MQL5 backward compatible with MQL4?
And the answer is no.
Again this is not accurate information.
It has been proven already and confirmed that the two languages are not compatible.
In the mql5.com codebase section you can find NUMEROUS EA and Indicators which will not work with what you are suggesting.
For example: https://www.mql5.com/en/code/11739
The above link is to an MQL4 based EA which processes offline Renko charts.
(Not my EA, just a random selection from the code base.)
This ABSOLUTELY will not run using the third party library work around as you suggest.
(Sorry about the RED color, but my screenshot application requires I either use RED, BLUE, or GREEN for Text. I can't change it.)
The platforms are not the same, nor are they intended to be. MQL4 and MQL5 is not compatible.
Please stop giving false information to people.
Right! Platforms differ, so even GUIs are different. And if you use platform differences, then there will be incompatibility. For example, CopyTicks or WinAPI.
But where platforms coincide, the differences in languages can be completely leveled by a single line in the code.
Please follow your own recommendation.
You said all someone needed to do is add one line. This is what I am talking about.
You cannot just tell someone to add one line and their code will work.
That is an absolute lie because you cannot do as you instruct.
You also ignored the fact that there are two additional libraries above the conversion library, which ARE NOT available for MT5 as installed.
That is a brand new installation of MT5, and that is the one of the points you refuse to understand or accept.
MQL4 is NOT language compatible with MQL5. The code does not directly translate nor work without modification between the two platforms.
I've given you numerous examples where they are vastly different.
Just because you want to be right, does not mean that you are.
You are wrong. You are providing false information to people, please stop it.
The CodeBase is even integrated in the metaeditor.
In most cases there is no need to consider compatibility on a large scale which would comprise entire platforms. In the real world this (complete compatibility) is not the case for all software, including Windows, Android OSes, etc. So repeating the mantra about complete incompatibility between MT4 and MT5 is just NOT TRUE.
In context of specific tasks (specific EAs, indicators, scripts) we can find sufficient level of compatiblity. Indeed, there exist specific codes which are not compatible between MT4 and MT5, but this is neither universal law nor proof of full incompatiblity.
As for including libraries, I'd note that both MT4 and MT5 rely on large set of built-in APIs and headers, they constantly change and become incompatible with previous versions from time to time. So dealing with proper headers is a must for those who intend to compile EA or indicator from source.