99 lines
3 KiB
MQL5
99 lines
3 KiB
MQL5
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//+------------------------------------------------------------------+
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//| TemplateMax.mq5 |
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//| Copyright 2021, MetaQuotes Ltd. |
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//| https://www.mql5.com |
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//+------------------------------------------------------------------+
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/*
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The following overloaded function template with 'const T &' parameters
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is required to accept classes/structs as its arguments.
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Otherwise we get multiple errors, such as:
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'objects are passed by reference only' and
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'ambiguous call to overloaded function with the same parameters'
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*/
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template<typename T>
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T Max(T value1, T value2)
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{
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Print(__FUNCSIG__, " T=", typename(T));
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return value1 > value2 ? value1 : value2;
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}
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template<typename T>
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T Max(const T &value1, const T &value2, const bool ref = false)
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{
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Print(__FUNCSIG__, " T=", typename(T));
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return value1 > value2 ? value1 : value2;
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}
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/*
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// uncomment this for more specific version for pointers
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template<typename T>
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T *Max(T *value1, T *value2)
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{
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Print(__FUNCSIG__, " T=", typename(T));
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return value1 > value2 ? value1 : value2;
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}
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*/
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//+------------------------------------------------------------------+
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//| Example of a struct |
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//+------------------------------------------------------------------+
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struct Dummy
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{
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int x;
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bool operator>(const Dummy &other) const
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{
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return x > other.x;
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}
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};
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//+------------------------------------------------------------------+
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//| Example of a class |
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//+------------------------------------------------------------------+
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class Data
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{
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public:
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int x;
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bool operator>(const Data &other) const
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{
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Print(__FUNCSIG__);
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return x > other.x;
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}
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};
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//+------------------------------------------------------------------+
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//| |
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//+------------------------------------------------------------------+
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void OnStart()
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{
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double d1 = 0, d2 = 1;
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datetime t1 = D'2020.01.01', t2 = D'2021.10.10';
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Print(Max(d1, d2));
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Print(Max(t1, t2));
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// ERROR:
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// template parameter ambiguous, could be 'double' or 'datetime'
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// Print(Max(d1, t1));
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Print(Max<ulong>(1000, 10000000));
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Dummy object1 = {}, object2 = {};
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Max(object1, object2);
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// ERRORs (before overloads are added):
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// if only the following function is presented
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// T Max(T value1, T value2)
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// 'object1' - objects are passed by reference only
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// 'Max' - cannot to apply template
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// Without overload T *Max(T *value1, T *value2)
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// the following code will call T Max(const T &value1, const T &value2)
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// with T=Data*
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Data *pointer1 = new Data();
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Data *pointer2 = new Data();
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Data *m = Max(pointer1, pointer2);
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delete pointer1;
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delete pointer2;
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}
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//+------------------------------------------------------------------+
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