design - Where does idea that "inheritance is to be avoided" originate from? -

-

recently discussed defect mentioned here , 1 of parties said "yes, that's why books inheritance should avoided.

i've been using inheritance years , find useful , convenient in many design cases. i'm sure person arguing @ least misunderstood "books say".

is there idea inheritance kind of bad , should avoided? originate , can learn more?

i think might have meant inheritance can overused, in cases composition better solution. discussed in several books, e.g.

inheritance powerful way achieve code reuse, not best tool job. used inappropriately, leads fragile software. safe use inheritance within package, subclass , superclass implementations under control of same programmers. safe use inheritance when extending classes designed , documented extension (item 17). inheriting ordinary concrete classes across package boundaries, however, dangerous. reminder, book uses word “inheritance” mean implementation inheritance (when 1 class extends another). problems discussed in item not apply interface inheritance (when class implements interface or 1 interface extends another).

unlike method invocation, inheritance violates encapsulation [snyder86]. in other words, subclass depends on implementation details of superclass proper function. superclass’s implementation may change release release, , if does, subclass may break, though code has not been touched. consequence, subclass must evolve in tandem superclass, unless superclass’s authors have designed , documented purpose of being extended.

  • effective c++ 3rd edition has several items related this:
    • item 32: make sure public inheritance models "is-a."
    • item 34: differentiate between inheritance of interface , inheritance of implementation
    • item 38: model "has-a" or "is-implemented-in-terms-of" through composition

Comments

Post a Comment

Popular posts from this blog

python - Scipy curvefit RuntimeError:Optimal parameters not found: Number of calls to function has reached maxfev = 1000 -

-
Image
i want make logharitmic fit. keep getting runtime error: optimal parameters not found: number of calls function has reached maxfev = 1000 i use following script. can tell me go wrong? use spyder still beginner. import math import matplotlib mpl scipy.optimize import curve_fit import numpy np #data f1=[735.0,696.0,690.0,683.0,680.0,678.0,679.0,675.0,671.0,669.0,668.0,664.0,664.0] t1=[1,90000.0,178200.0,421200.0,505800.0,592200.0,768600.0,1036800.0,1371600.0,1630800.0,1715400.0,2345400.0,2409012.0] f1n=np.array(f1) t1n=np.array(t1) plt.plot(t1,f1,'ro',label="original data") # curvefit def func(t,a,b): return a+b*np.log(t) t=np.linspace(0,3600*24*28,13) popt, pcov = curve_fit(func, t, f1n, maxfev=1000) plt.plot(t, func(t, *popt), label="fitted curve") plt.legend(loc='upper left') plt.show() your original data t1 , f1 . therefore curve_fit should given t1 second argument, not t . popt, pcov = curve_fit(func,...
Read more

binding - How can you make the color of elements of a WPF DrawingImage dynamic? -

-
we have need make vector graphic images change color of elements within graphic @ runtime. seem setting colors based on either static or dynamic resource values wouldn't work. want have multiple versions of same graphic, each abilty set graphic elements (path, line, etc) different colors don't think dynamic resource approach work. leaves data binding seems right approach. update graphic use data binding expr instead of hard-coded brush color so: <drawingimage x:key="graphic1"> <drawingimage.drawing> <drawinggroup> <drawinggroup.children> <geometrydrawing geometry="f1 m 8.4073,23.9233l"> <geometrydrawing.pen> <pen linejoin="round" brush="{binding line1brush, mode=oneway}"/> </geometrydrawing.pen> </geometrydrawing> <geometrydrawing geometry="f1 m 3.6875,2.56251l"> <geometrydrawing....
Read more

c# - How to add a new treeview at the selected node? -

-
i have treeview 4 levels; parent, child, grandchild, great-grandchild. selectednode @ grandchild level. what i'm trying create new "treeview" @ grandchild - no, dont wnat create new node "selectednode" (grandchild). should somelike this: parent child grandchild (new treeview) parent grandchild great-grandchild child great-grandchild child grandchild grandchild it similar parent table mother , father went off , had new childern different spouse other spouse of there existing children. private sub populaterootlevel() ' query find first round of parent populatenodes(dt, jcatreeview.nodes) end sub private sub populatenodes(byval dt datatable, byval nodes treenodecollection) each dr datarow in dt.rows dim tn new treenode() tn.text = dr("title").tostring()...
Read more